Implement Enumerable.Reverse(TSource[]) (#107957)

Closes #107723.
dotnet · Sep 25, 2024 · d6ac24c · d6ac24c
1 parent cf165a7
commit d6ac24c
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Showing 5 changed files with 54 additions and 1 deletion.
diff --git a/src/libraries/System.Linq.Queryable/tests/Queryable.cs b/src/libraries/System.Linq.Queryable/tests/Queryable.cs
@@ -96,6 +96,7 @@ public static void MatchSequencePattern()
  nameof(Enumerable.Prepend),
  nameof(Enumerable.ToHashSet),
  nameof(Enumerable.TryGetNonEnumeratedCount),
+ nameof(Enumerable.Reverse),
  "Fold",
  "LeftJoin",
  }

diff --git a/src/libraries/System.Linq/ref/System.Linq.cs b/src/libraries/System.Linq/ref/System.Linq.cs
@@ -159,6 +159,7 @@ public static System.Collections.Generic.IEnumerable<
  public static System.Collections.Generic.IEnumerable<int> Range(int start, int count) { throw null; }
  public static System.Collections.Generic.IEnumerable<TResult> Repeat<TResult>(TResult element, int count) { throw null; }
  public static System.Collections.Generic.IEnumerable<TSource> Reverse<TSource>(this System.Collections.Generic.IEnumerable<TSource> source) { throw null; }
+ public static System.Collections.Generic.IEnumerable<TSource> Reverse<TSource>(this TSource[] source) { throw null; }
  public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
  public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, int, System.Collections.Generic.IEnumerable<TResult>> selector) { throw null; }
  public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource, TCollection, TResult>(this System.Collections.Generic.IEnumerable<TSource> source, System.Func<TSource, System.Collections.Generic.IEnumerable<TCollection>> collectionSelector, System.Func<TSource, TCollection, TResult> resultSelector) { throw null; }

diff --git a/src/libraries/System.Linq/src/System/Linq/Reverse.cs b/src/libraries/System.Linq/src/System/Linq/Reverse.cs
@@ -23,6 +23,21 @@ public static IEnumerable<TSource> Reverse<TSource>(this IEnumerable<TSource> so
  return new ReverseIterator<TSource>(source);
  }
 
+ public static IEnumerable<TSource> Reverse<TSource>(this TSource[] source)
+ {
+ if (source is null)
+ {
+ ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
+ }
+
+ if (source.Length == 0)
+ {
+ return [];
+ }
+
+ return new ReverseIterator<TSource>(source);
+ }
+
  /// <summary>
  /// An iterator that yields the items of an <see cref="IEnumerable{TSource}"/> in reverse.
  /// </summary>

diff --git a/src/libraries/System.Linq/tests/ConsistencyTests.cs b/src/libraries/System.Linq/tests/ConsistencyTests.cs
@@ -44,6 +44,7 @@ private static IEnumerable<string> GetExcludedMethods()
  nameof(Enumerable.ToList),
  nameof(Enumerable.ToHashSet),
  nameof(Enumerable.TryGetNonEnumeratedCount),
+ nameof(Enumerable.Reverse),
  "Fold",
  "LeftJoin",
  };

diff --git a/src/libraries/System.Linq/tests/ReverseTests.cs b/src/libraries/System.Linq/tests/ReverseTests.cs
@@ -11,7 +11,8 @@ public class ReverseTests : EnumerableTests
  [Fact]
  public void InvalidArguments()
  {
- AssertExtensions.Throws<ArgumentNullException>("source", () => Enumerable.Reverse<string>(null));
+ AssertExtensions.Throws<ArgumentNullException>("source", () => Enumerable.Reverse<string>((IEnumerable<string>)null));
+ AssertExtensions.Throws<ArgumentNullException>("source", () => Enumerable.Reverse<string>((string[])null));
  }
 
  [Theory]
@@ -48,6 +49,40 @@ public void Reverse<T>(IEnumerable<T> source)
  Assert.Equal(actual, actual); // Repeat the enumeration against itself.
  }
 
+ [Theory]
+ [MemberData(nameof(ReverseData))]
+ public void ReverseArray<T>(IEnumerable<T> source)
+ {
+ T[] expected = source.ToArray();
+ Array.Reverse(expected);
+
+ IEnumerable<T> actual = source.ToArray().Reverse();
+
+ Assert.Equal(expected, actual);
+ Assert.Equal(expected.Count(), actual.Count()); // Count may be optimized.
+ Assert.Equal(expected, actual.ToArray());
+ Assert.Equal(expected, actual.ToList());
+
+ Assert.Equal(expected.FirstOrDefault(), actual.FirstOrDefault());
+ Assert.Equal(expected.LastOrDefault(), actual.LastOrDefault());
+
+ for (int i = 0; i < expected.Length; i++)
+ {
+ Assert.Equal(expected[i], actual.ElementAt(i));
+
+ Assert.Equal(expected.Skip(i), actual.Skip(i));
+ Assert.Equal(expected.Take(i), actual.Take(i));
+ }
+
+ Assert.Equal(default(T), actual.ElementAtOrDefault(-1));
+ Assert.Equal(default(T), actual.ElementAtOrDefault(expected.Length));
+
+ Assert.Equal(expected, actual.Select(_ => _));
+ Assert.Equal(expected, actual.Where(_ => true));
+
+ Assert.Equal(actual, actual); // Repeat the enumeration against itself.
+ }
+
  [Theory, MemberData(nameof(ReverseData))]
  public void RunOnce<T>(IEnumerable<T> source)
  {