Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs#121998

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eiriktsarpalis merged 7 commits into from
Apr 6, 2026
Merged

Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs #121998

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7a75525
Initial plan
Copilot Nov 26, 2025
dd8a7d8
Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…
Copilot Nov 26, 2025
afae193
Add tests for Join/LeftJoin/RightJoin tuple overloads
Copilot Nov 26, 2025
95b9985
Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…
Copilot Nov 27, 2025
078849d
Improve tests
roji Apr 3, 2026
ed2cd44
Address review feedback: fix XML docs for optional comparer and stren…
roji Apr 4, 2026
09a802d
Merge branch 'main' into copilot/add-linq-join-return-tuple
eiriktsarpalis Apr 6, 2026
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6 changes: 6 additions & 0 deletions src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs
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Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down
135 changes: 135 additions & 0 deletions src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs
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Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
}
}
}

/// <summary>Correlates the elements of two sequences based on matching keys.</summary>
/// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
/// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
/// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
/// <param name="outer">The first sequence to join.</param>
/// <param name="inner">The sequence to join to the first sequence.</param>
/// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
/// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
/// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
/// <returns>
/// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
/// that are obtained by performing an inner join on two sequences.
/// </returns>
/// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
this IAsyncEnumerable<TOuter> outer,
IAsyncEnumerable<TInner> inner,
Func<TOuter, TKey> outerKeySelector,
Func<TInner, TKey> innerKeySelector,
IEqualityComparer<TKey>? comparer = null)
{
ArgumentNullException.ThrowIfNull(outer);
ArgumentNullException.ThrowIfNull(inner);
ArgumentNullException.ThrowIfNull(outerKeySelector);
ArgumentNullException.ThrowIfNull(innerKeySelector);

return
outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
Func<TOuter, TKey> outerKeySelector,
Func<TInner, TKey> innerKeySelector,
IEqualityComparer<TKey>? comparer,
[EnumeratorCancellation] CancellationToken cancellationToken)
{
await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

if (await e.MoveNextAsync())
{
AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
if (lookup.Count != 0)
{
do
{
TOuter item = e.Current;
Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
if (g is not null)
{
int count = g._count;
TInner[] elements = g._elements;
for (int i = 0; i != count; ++i)
{
yield return (item, elements[i]);
}
}
}
while (await e.MoveNextAsync());
}
}
}
}

/// <summary>Correlates the elements of two sequences based on matching keys.</summary>
/// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
/// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
/// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
/// <param name="outer">The first sequence to join.</param>
/// <param name="inner">The sequence to join to the first sequence.</param>
/// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
/// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
/// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
/// <returns>
/// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
/// that are obtained by performing an inner join on two sequences.
/// </returns>
/// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
/// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
this IAsyncEnumerable<TOuter> outer,
IAsyncEnumerable<TInner> inner,
Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
IEqualityComparer<TKey>? comparer = null)
{
ArgumentNullException.ThrowIfNull(outer);
ArgumentNullException.ThrowIfNull(inner);
ArgumentNullException.ThrowIfNull(outerKeySelector);
ArgumentNullException.ThrowIfNull(innerKeySelector);

return
outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
IAsyncEnumerable<TOuter> outer,
IAsyncEnumerable<TInner> inner,
Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
IEqualityComparer<TKey>? comparer,
[EnumeratorCancellation] CancellationToken cancellationToken)
{
await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

if (await e.MoveNextAsync())
{
AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
if (lookup.Count != 0)
{
do
{
TOuter item = e.Current;
Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
if (g is not null)
{
int count = g._count;
TInner[] elements = g._elements;
for (int i = 0; i != count; ++i)
{
yield return (item, elements[i]);
}
}
}
while (await e.MoveNextAsync());
}
}
}
}
}
}
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}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs#121998

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 Merged

eiriktsarpalis
merged 7 commits into

from

Apr 6, 2026
 Merged


Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
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7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
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injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
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 Merged

eiriktsarpalis
merged 7 commits into

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Apr 6, 2026
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Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
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7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs#121998

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 Merged

eiriktsarpalis
merged 7 commits into

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Apr 6, 2026
 Merged


Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
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7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
Loading
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

Skip to content
Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs#121998

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

 Sign up for GitHub

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privacy statement. We’ll occasionally send you account related emails.

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to your account

 Merged

eiriktsarpalis
merged 7 commits into

from

Apr 6, 2026
 Merged


Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
Show file tree
Hide file tree
 Changes from all commits
Commits

Show all changes


7 commits


Select commit
Hold shift + click to select a range
7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
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injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
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 Merged

eiriktsarpalis
merged 7 commits into

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Apr 6, 2026
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Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
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7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
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injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
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eiriktsarpalis
merged 7 commits into

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Apr 6, 2026
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Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
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7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
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, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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 Merged

eiriktsarpalis
merged 7 commits into

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Apr 6, 2026
 Merged


Add Join/LeftJoin/RightJoin tuple overloads to LINQ APIs
#121998
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7a75525

Initial plan


Copilot Nov 26, 2025
dd8a7d8

Add Join/LeftJoin/RightJoin tuple overloads to Enumerable, Queryable,…


Copilot Nov 26, 2025
afae193

Add tests for Join/LeftJoin/RightJoin tuple overloads


Copilot Nov 26, 2025
95b9985

Consolidate Join/LeftJoin/RightJoin tuple overloads to use optional c…


Copilot Nov 27, 2025
078849d

Improve tests


roji Apr 3, 2026
ed2cd44

Address review feedback: fix XML docs for optional comparer and stren…


roji Apr 4, 2026
09a802d

Merge branch 'main' into copilot/add-linq-join-return-tuple


eiriktsarpalis Apr 6, 2026

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6 changes: 6 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/ref/System.Linq.AsyncEnumerable.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -81,6 +81,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Intersect<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> first, System.Collections.Generic.IAsyncEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> Join<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<TSource> LastAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -92,6 +94,8 @@ public static partial class AsyncEnumerable
 public static System.Threading.Tasks.ValueTask<TSource> LastOrDefaultAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, TSource defaultValue, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter, TInner?, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> LeftJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter, TInner?, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter Outer, TInner? Inner)> LeftJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, bool> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<bool>> predicate, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
 public static System.Threading.Tasks.ValueTask<long> LongCountAsync<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
Expand All@@ -114,6 +118,8 @@ public static partial class AsyncEnumerable
 public static System.Collections.Generic.IAsyncEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IAsyncEnumerable<TSource> source) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Func<TOuter?, TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TResult>> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> RightJoin<TOuter, TInner, TKey, TResult>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Func<TOuter?, TInner, TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> outerKeySelector, System.Func<TInner, System.Threading.CancellationToken, System.Threading.Tasks.ValueTask<TKey>> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<(TOuter? Outer, TInner Inner)> RightJoin<TOuter, TInner, TKey>(this System.Collections.Generic.IAsyncEnumerable<TOuter> outer, System.Collections.Generic.IAsyncEnumerable<TInner> inner, System.Func<TOuter, TKey> outerKeySelector, System.Func<TInner, TKey> innerKeySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer = null) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
 public static System.Collections.Generic.IAsyncEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IAsyncEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IAsyncEnumerable<TResult>> selector) { throw null; }
Expand Down

135 changes: 135 additions & 0 deletions
src/libraries/System.Linq.AsyncEnumerable/src/System/Linq/Join.cs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -156,5 +156,140 @@ static async IAsyncEnumerable<TResult> Impl(
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer, IAsyncEnumerable<TInner> inner,
 Func<TOuter, TKey> outerKeySelector,
 Func<TInner, TKey> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(outerKeySelector(item), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }

 /// <summary>Correlates the elements of two sequences based on matching keys.</summary>
 /// <typeparam name="TOuter">The type of the elements of the first sequence.</typeparam>
 /// <typeparam name="TInner">The type of the elements of the second sequence.</typeparam>
 /// <typeparam name="TKey">The type of the keys returned by the key selector functions.</typeparam>
 /// <param name="outer">The first sequence to join.</param>
 /// <param name="inner">The sequence to join to the first sequence.</param>
 /// <param name="outerKeySelector">A function to extract the join key from each element of the first sequence.</param>
 /// <param name="innerKeySelector">A function to extract the join key from each element of the second sequence.</param>
 /// <param name="comparer">An <see cref="IEqualityComparer{T}"/> to use to hash and compare keys.</param>
 /// <returns>
 /// An <see cref="IAsyncEnumerable{T}"/> that has elements of type <c>(TOuter Outer, TInner Inner)</c>
 /// that are obtained by performing an inner join on two sequences.
 /// </returns>
 /// <exception cref="ArgumentNullException"><paramref name="outer" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="inner" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="outerKeySelector" /> is <see langword="null" />.</exception>
 /// <exception cref="ArgumentNullException"><paramref name="innerKeySelector" /> is <see langword="null" />.</exception>
 public static IAsyncEnumerable<(TOuter Outer, TInner Inner)> Join<TOuter, TInner, TKey>(
 this IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer = null)
 {
 ArgumentNullException.ThrowIfNull(outer);
 ArgumentNullException.ThrowIfNull(inner);
 ArgumentNullException.ThrowIfNull(outerKeySelector);
 ArgumentNullException.ThrowIfNull(innerKeySelector);

 return
 outer.IsKnownEmpty() || inner.IsKnownEmpty() ? Empty<(TOuter Outer, TInner Inner)>() :
 Impl(outer, inner, outerKeySelector, innerKeySelector, comparer, default);

 static async IAsyncEnumerable<(TOuter Outer, TInner Inner)> Impl(
 IAsyncEnumerable<TOuter> outer,
 IAsyncEnumerable<TInner> inner,
 Func<TOuter, CancellationToken, ValueTask<TKey>> outerKeySelector,
 Func<TInner, CancellationToken, ValueTask<TKey>> innerKeySelector,
 IEqualityComparer<TKey>? comparer,
 [EnumeratorCancellation] CancellationToken cancellationToken)
 {
 await using IAsyncEnumerator<TOuter> e = outer.GetAsyncEnumerator(cancellationToken);

 if (await e.MoveNextAsync())
 {
 AsyncLookup<TKey, TInner> lookup = await AsyncLookup<TKey, TInner>.CreateForJoinAsync(inner, innerKeySelector, comparer, cancellationToken);
 if (lookup.Count != 0)
 {
 do
 {
 TOuter item = e.Current;
 Grouping<TKey, TInner>? g = lookup.GetGrouping(await outerKeySelector(item, cancellationToken), create: false);
 if (g is not null)
 {
 int count = g._count;
 TInner[] elements = g._elements;
 for (int i = 0; i != count; ++i)
 {
 yield return (item, elements[i]);
 }
 }
 }
 while (await e.MoveNextAsync());
 }
 }
 }
 }
 }
}
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