QueryableExtensions.cs

namespace System.Linq
{
 using System;
 using System.Linq.Expressions;
 using System.Reflection;

 internal static class QueryableExtensions
 {
 public static TSource ElementAt<TSource>(this IQueryable<TSource> source, Index index)
 {
 if (source == null)
 // throw Error.ArgumentNull(nameof(source));
 throw new ArgumentNullException(nameof(source));
 return source.Provider.Execute<TSource>(
 Expression.Call(
 null,
 CachedReflectionInfo.ElementAt_TSource_2(typeof(TSource)),
 source.Expression, Expression.Constant(index)
 ));
 }

 public static TSource ElementAtOrDefault<TSource>(this IQueryable<TSource> source, Index index)
 {
 if (source == null)
 // throw Error.ArgumentNull(nameof(source));
 throw new ArgumentNullException(nameof(source));
 return source.Provider.Execute<TSource>(
 Expression.Call(
 null,
 CachedReflectionInfo.ElementAtOrDefault_TSource_2(typeof(TSource)),
 source.Expression, Expression.Constant(index)
 ));
 }

 public static IQueryable<TSource> ElementsIn<TSource>(this IQueryable<TSource> source, Range range)
 {
 if (source == null)
 // throw Error.ArgumentNull(nameof(source));
 throw new ArgumentNullException(nameof(source));

 return source.Provider.CreateQuery<TSource>(
 Expression.Call(
 null,
 CachedReflectionInfo.ElementsIn_TSource_2(typeof(TSource)),
 source.Expression, Expression.Constant(range)));
 }

 public static IQueryable<TSource> Slice<TSource>(this IQueryable<TSource> source, Range range)
 {
 if (source == null)
 // throw Error.ArgumentNull(nameof(source));
 throw new ArgumentNullException(nameof(source));

 return source.Provider.CreateQuery<TSource>(
 Expression.Call(
 null,
 CachedReflectionInfo.Slice_TSource_2(typeof(TSource)),
 source.Expression, Expression.Constant(range)));
 }
 }

 internal static class CachedReflectionInfo
 {
 private static MethodInfo? s_ElementAt_TSource_2;

 public static MethodInfo ElementAt_TSource_2(Type TSource) =>
 (s_ElementAt_TSource_2 ??= new Func<IQueryable<object>, Index, object>(QueryableExtensions.ElementAt).GetMethodInfo().GetGenericMethodDefinition())
 .MakeGenericMethod(TSource);

 private static MethodInfo? s_ElementAtOrDefault_TSource_2;

 public static MethodInfo ElementAtOrDefault_TSource_2(Type TSource) =>
 (s_ElementAtOrDefault_TSource_2 ??= new Func<IQueryable<object>, Index, object>(QueryableExtensions.ElementAtOrDefault).GetMethodInfo().GetGenericMethodDefinition())
 .MakeGenericMethod(TSource);

 private static MethodInfo? s_ElementsIn_TSource_2;

 public static MethodInfo ElementsIn_TSource_2(Type TSource) =>
 (s_ElementsIn_TSource_2 ??= new Func<IQueryable<object>, Range, IQueryable<object>>(QueryableExtensions.ElementsIn).GetMethodInfo().GetGenericMethodDefinition())
 .MakeGenericMethod(TSource);

 private static MethodInfo? s_Slice_TSource_2;

 public static MethodInfo Slice_TSource_2(Type TSource) =>
 (s_Slice_TSource_2 ??= new Func<IQueryable<object>, Range, IQueryable<object>>(QueryableExtensions.ElementsIn).GetMethodInfo().GetGenericMethodDefinition())
 .MakeGenericMethod(TSource);
 }
}