EnumerateLines

api_list.include.md

@@ -168,6 +168,7 @@
 #### ReadOnlySpan<Char>
 
  * `Boolean EndsWith(String, StringComparison)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.endswith#system-memoryextensions-endswith-1(system-readonlyspan((-0))-system-readonlyspan((-0))))
+ * `SpanLineEnumerator EnumerateLines()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.enumeratelines#system-memoryextensions-enumeratelines(system-readonlyspan((system-char))))
  * `Boolean SequenceEqual(String)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.sequenceequal#system-memoryextensions-sequenceequal-1(system-readonlyspan((-0))-system-readonlyspan((-0))))
  * `Boolean StartsWith(String, StringComparison)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.startswith#system-memoryextensions-startswith-1(system-readonlyspan((-0))-system-readonlyspan((-0))))
 
@@ -226,6 +227,7 @@
 #### Span<Char>
 
  * `Boolean EndsWith(String)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.endswith#system-memoryextensions-endswith-1(system-span((-0))-system-readonlyspan((-0))))
+ * `SpanLineEnumerator EnumerateLines()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.enumeratelines#system-memoryextensions-enumeratelines(system-span((system-char))))
  * `Boolean SequenceEqual(String)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.sequenceequal#system-memoryextensions-sequenceequal-1(system-span((-0))-system-readonlyspan((-0))))
  * `Boolean StartsWith(String)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.startswith#system-memoryextensions-startswith-1(system-span((-0))-system-readonlyspan((-0))))
 

src/Consume/Consume.cs

@@ -205,6 +205,13 @@ public void ListAddRangeReadOnlySpan()
         list.AddRange("ab".AsSpan());
     }
 
+    public void EnumerateLinesReadOnlySpan()
+    {
+        foreach (var line in "ab".AsSpan().EnumerateLines())
+        {
+        }
+    }
+
     public void ListInsertRangeReadOnlySpan()
     {
         var list = new List<char>

src/Polyfill/Polyfill_Memory.cs

@@ -2,7 +2,7 @@
 
 #pragma warning disable
 
-#if FeatureMemory && (NETFRAMEWORK || NETSTANDARD || NETCOREAPP2X)
+#if FeatureMemory
 
 using System;
 using System.Collections.Generic;
@@ -12,6 +12,41 @@
 
 static partial class Polyfill
 {
+
+#if !NET6_0_OR_GREATER
+
+    /// <summary>
+    /// Returns an enumeration of lines over the provided span.
+    /// </summary>
+    /// <remarks>
+    /// It is recommended that protocol parsers not utilize this API. See the documentation
+    /// for <see cref="string.ReplaceLineEndings"/> for more information on how newline
+    /// sequences are detected.
+    /// </remarks>
+    [Link("https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.enumeratelines#system-memoryextensions-enumeratelines(system-readonlyspan((system-char)))")]
+    public static SpanLineEnumerator EnumerateLines(this ReadOnlySpan<char> span)
+    {
+        return new SpanLineEnumerator(span);
+    }
+
+    /// <summary>
+    /// Returns an enumeration of lines over the provided span.
+    /// </summary>
+    /// <remarks>
+    /// It is recommended that protocol parsers not utilize this API. See the documentation
+    /// for <see cref="string.ReplaceLineEndings"/> for more information on how newline
+    /// sequences are detected.
+    /// </remarks>
+    [Link("https://learn.microsoft.com/en-us/dotnet/api/system.memoryextensions.enumeratelines#system-memoryextensions-enumeratelines(system-span((system-char)))")]
+    public static SpanLineEnumerator EnumerateLines(this Span<char> span)
+    {
+        return new SpanLineEnumerator(span);
+    }
+
+#endif
+
+#if NETFRAMEWORK || NETSTANDARD || NETCOREAPP2X
+
     /// <summary>
     /// Indicates whether a specified value is found in a read-only span. Values are compared using IEquatable{T}.Equals(T).
     /// </summary>
@@ -131,6 +166,9 @@ public static bool EndsWith(
         this Span<char> target,
         string other) =>
         target.EndsWith(other.AsSpan());
+
+#endif
+
 }
 
 #endif

src/Polyfill/SpanLineEnumerator.cs

@@ -0,0 +1,92 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// <auto-generated />
+
+#pragma warning disable
+
+#if FeatureMemory && !NET6_0_OR_GREATER
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Runtime.InteropServices;
+using Link = System.ComponentModel.DescriptionAttribute;
+
+namespace System.Text;
+
+/// <summary>
+/// Enumerates the lines of a <see cref="ReadOnlySpan{Char}"/>.
+/// </summary>
+/// <remarks>
+/// To get an instance of this type, use <see cref="MemoryExtensions.EnumerateLines(ReadOnlySpan{char})"/>.
+/// </remarks>
+[Link("https://learn.microsoft.com/en-us/dotnet/api/system.text.spanlineenumerator")]
+public ref struct SpanLineEnumerator
+{
+    private ReadOnlySpan<char> _remaining;
+    private ReadOnlySpan<char> _current;
+    private bool _isEnumeratorActive;
+    ReadOnlySpan<char> newlines = "\r\f\u0085\u2028\u2029\n".AsSpan();
+
+    internal SpanLineEnumerator(ReadOnlySpan<char> buffer)
+    {
+        _remaining = buffer;
+        _current = default;
+        _isEnumeratorActive = true;
+    }
+
+    /// <summary>
+    /// Gets the line at the current position of the enumerator.
+    /// </summary>
+    public ReadOnlySpan<char> Current => _current;
+
+    /// <summary>
+    /// Returns this instance as an enumerator.
+    /// </summary>
+    public SpanLineEnumerator GetEnumerator() => this;
+
+    /// <summary>
+    /// Advances the enumerator to the next line of the span.
+    /// </summary>
+    /// <returns>
+    /// True if the enumerator successfully advanced to the next line; false if
+    /// the enumerator has advanced past the end of the span.
+    /// </returns>
+    public bool MoveNext()
+    {
+        if (!_isEnumeratorActive)
+        {
+            // EOF previously reached or enumerator was never initialized
+            return false;
+        }
+
+        var remaining = _remaining;
+        //TODO: revisit when SearchValues is implemented
+        var idx = remaining.IndexOfAny(newlines);
+
+        if ((uint)idx < (uint)remaining.Length)
+        {
+            var stride = 1;
+
+            if (remaining[idx] == '\r' && (uint)(idx + 1) < (uint)remaining.Length && remaining[idx + 1] == '\n')
+            {
+                stride = 2;
+            }
+
+            _current = remaining[..idx];
+            _remaining = remaining[(idx + stride)..];
+        }
+        else
+        {
+            // We've reached EOF, but we still need to return 'true' for this final
+            // iteration so that the caller can query the Current property once more.
+
+            _current = remaining;
+            _remaining = default;
+            _isEnumeratorActive = false;
+        }
+
+        return true;
+    }
+}
+#endif

src/Tests/PolyfillTests_Memory.cs

@@ -58,6 +58,23 @@ public void ReadOnlySpan_ZeroLengthContains_String()
         Assert.False(found);
     }
 
+    [Test]
+    public void ReadOnlySpan_EnumerateLines()
+    {
+        var list = new List<string>();
+        var input = """
+                    a
+                    b
+                    """;
+        foreach (var line in input.AsSpan().EnumerateLines())
+        {
+            list.Add(line.ToString());
+        }
+
+        Assert.Equals("a", list[0]);
+        Assert.Equals("b", list[1]);
+    }
+
     [Test]
     public void ReadOnlySpan_TestMatchContains_String()
     {