Add foreach support to Span<T> and ReadOnlySpan<T> (#14922)

Adds a ref struct Enumerator, and a corresponding GetEnumerator method to each.

diff --git a/src/mscorlib/shared/System/ReadOnlySpan.cs b/src/mscorlib/shared/System/ReadOnlySpan.cs
index a0a0cf9..9f491f6 100644 (file)
--- a/src/mscorlib/shared/System/ReadOnlySpan.cs
+++ b/src/mscorlib/shared/System/ReadOnlySpan.cs
@@ -322,5 +322,60 @@ namespace System
         /// Returns a 0-length read-only span whose base is the null pointer.
         /// </summary>
         public static ReadOnlySpan<T> Empty => default(ReadOnlySpan<T>);
+
+        /// <summary>Gets an enumerator for this span.</summary>
+        public Enumerator GetEnumerator() => new Enumerator(this);
+
+        /// <summary>Enumerates the elements of a <see cref="ReadOnlySpan{T}"/>.</summary>
+        public ref struct Enumerator
+        {
+            /// <summary>The span being enumerated.</summary>
+            private readonly ReadOnlySpan<T> _span;
+            /// <summary>The next index to yield.</summary>
+            private int _index;
+
+            /// <summary>Initialize the enumerator.</summary>
+            /// <param name="span">The span to enumerate.</param>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            internal Enumerator(ReadOnlySpan<T> span)
+            {
+                _span = span;
+                _index = -1;
+            }
+
+            /// <summary>Advances the enumerator to the next element of the span.</summary>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public bool MoveNext()
+            {
+                int index = _index + 1;
+                if (index < _span.Length)
+                {
+                    _index = index;
+                    return true;
+                }
+
+                return false;
+            }
+
+            /// <summary>Gets the element at the current position of the enumerator.</summary>
+            public ref readonly T Current
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                get
+                {
+                    // TODO https://github.com/dotnet/coreclr/pull/14727:
+                    // Change this to simply be:
+                    //     get => ref readonly _span[_index];
+                    // once ReadOnlySpan<T>'s indexer returns ref readonly.
+
+                    if ((uint)_index >= (uint)_span.Length)
+                    {
+                        ThrowHelper.ThrowIndexOutOfRangeException();
+                    }
+
+                    return ref Unsafe.Add(ref _span.DangerousGetPinnableReference(), _index);
+                }
+            }
+        }
     }
 }

diff --git a/src/mscorlib/shared/System/Span.cs b/src/mscorlib/shared/System/Span.cs
index f885c63..aec83de 100644 (file)
--- a/src/mscorlib/shared/System/Span.cs
+++ b/src/mscorlib/shared/System/Span.cs
@@ -409,5 +409,47 @@ namespace System
         /// Returns an empty <see cref="Span{T}"/>
         /// </summary>
         public static Span<T> Empty => default(Span<T>);
+
+        /// <summary>Gets an enumerator for this span.</summary>
+        public Enumerator GetEnumerator() => new Enumerator(this);
+
+        /// <summary>Enumerates the elements of a <see cref="Span{T}"/>.</summary>
+        public ref struct Enumerator
+        {
+            /// <summary>The span being enumerated.</summary>
+            private readonly Span<T> _span;
+            /// <summary>The next index to yield.</summary>
+            private int _index;
+
+            /// <summary>Initialize the enumerator.</summary>
+            /// <param name="span">The span to enumerate.</param>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            internal Enumerator(Span<T> span)
+            {
+                _span = span;
+                _index = -1;
+            }
+
+            /// <summary>Advances the enumerator to the next element of the span.</summary>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public bool MoveNext()
+            {
+                int index = _index + 1;
+                if (index < _span.Length)
+                {
+                    _index = index;
+                    return true;
+                }
+
+                return false;
+            }
+
+            /// <summary>Gets the element at the current position of the enumerator.</summary>
+            public ref T Current
+            {
+                [MethodImpl(MethodImplOptions.AggressiveInlining)]
+                get => ref _span[_index];
+            }
+        }
     }
 }