Description
C# 14 introduces new built-in span conversions and type inference rules making overloads with span parameters applicable in more scenarios.
However, Expression lambdas cannot be interpreted when they involve ref structs like Span and ReadOnlySpan. For example:
usingSystem;usingSystem.Linq;usingSystem.Linq.Expressions;Expression<Func<int[],int,bool>>exp=(array,num)=>array.Contains(num);exp.Compile(preferInterpretation:true);// fails at runtime in C# 14
The array.Contains binds to Enumerable.Contains in C# 13 but binds to MemoryExtensions.Contains in C# 14. The latter involves ReadOnlySpan and hence crashes when Expression.Compile(preferInterpretation: true) is called.
Version
.NET 10 Preview 1
Previous behavior
In C# 13 and earlier, an extension method taking a ReadOnlySpan<T> or Span<T> receiver is not applicable to a value of type T[]. Therefore, only non-span extension methods like the ones from the System.Linq.Enumerable class are usually bound inside Expression lambdas.
New behavior
In C# 14 and later, methods with ReadOnlySpan<T> or Span<T> parameters can participate in type inference or be used as extension methods in more scenarios. This makes span-based methods like the ones from the System.MemoryExtensions class bind in more scenarios, including inside Expression lambdas where they will cause runtime exceptions when compiled with interpretation.
Type of breaking change
Reason for change
The C# language feature allows simplified API design and usage (e.g., one ReadOnlySpan extension method can apply to both spans and arrays).
Recommended action
If you need to continue using Expression interpretation, you should make sure the non-span overloads are bound, e.g., by casting arguments to the exact types the method signature takes or calling the extension methods as explicit static invocations:
usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Linq.Expressions;M((array,num)=>array.Contains(num));// fails, binds to MemoryExtensions.ContainsM((array,num)=>((IEnumerable<int>)array).Contains(num));// ok, binds to Enumerable.ContainsM((array,num)=>array.AsEnumerable().Contains(num));// ok, binds to Enumerable.ContainsM((array,num)=>Enumerable.Contains(array,num));// ok, binds to Enumerable.ContainsvoidM(Expression<Func<int[],int,bool>>e)=>e.Compile(preferInterpretation:true);
Feature area
Other (please put exact area in description textbox)
Affected APIs
System.Linq.Expressions.Expression.Compile
Associated WorkItem - 360646
Description
C# 14 introduces new built-in span conversions and type inference rules making overloads with span parameters applicable in more scenarios.
However, Expression lambdas cannot be interpreted when they involve ref structs like Span and ReadOnlySpan. For example:
The
array.Containsbinds toEnumerable.Containsin C# 13 but binds toMemoryExtensions.Containsin C# 14. The latter involves ReadOnlySpan and hence crashes whenExpression.Compile(preferInterpretation: true)is called.Version
.NET 10 Preview 1
Previous behavior
In C# 13 and earlier, an extension method taking a
ReadOnlySpan<T>orSpan<T>receiver is not applicable to a value of typeT[]. Therefore, only non-span extension methods like the ones from theSystem.Linq.Enumerableclass are usually bound inside Expression lambdas.New behavior
In C# 14 and later, methods with
ReadOnlySpan<T>orSpan<T>parameters can participate in type inference or be used as extension methods in more scenarios. This makes span-based methods like the ones from theSystem.MemoryExtensionsclass bind in more scenarios, including inside Expression lambdas where they will cause runtime exceptions when compiled with interpretation.Type of breaking change
Reason for change
The C# language feature allows simplified API design and usage (e.g., one ReadOnlySpan extension method can apply to both spans and arrays).
Recommended action
If you need to continue using Expression interpretation, you should make sure the non-span overloads are bound, e.g., by casting arguments to the exact types the method signature takes or calling the extension methods as explicit static invocations:
Feature area
Other (please put exact area in description textbox)
Affected APIs
Associated WorkItem - 360646