From 0621c246a0db7e8ac07a8c4fad31ff2fbeff3163 Mon Sep 17 00:00:00 2001
From: Oliver Booth <me@olivr.me>
Date: Thu, 6 Apr 2023 02:31:22 +0100
Subject: [PATCH] feat: add Span<T>.Replace

---
 CHANGELOG.md                           |  1 +
 X10D.Tests/src/Collections/SpanTest.cs | 24 +++++++++++++++++++++++
 X10D/src/Collections/SpanExtensions.cs | 27 +++++++++++++++++++++++++-
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c978814..a0fcace 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - X10D: Added extension methods for `DateOnly`, for parity with `DateTime` and `DateTimeOffset`.
 - X10D: Added math-related extension methods for `BigInteger`.
+- X10D: Added `Span<T>.Replace(T, T)`.
 
 ### Changed
 - X10D: `DateTime.Age(DateTime)` and `DateTimeOffset.Age(DateTimeOffset)` parameter renamed from `asOf` to `referenceDate`.
diff --git a/X10D.Tests/src/Collections/SpanTest.cs b/X10D.Tests/src/Collections/SpanTest.cs
index 5df5acd..0c59d1c 100644
--- a/X10D.Tests/src/Collections/SpanTest.cs
+++ b/X10D.Tests/src/Collections/SpanTest.cs
@@ -46,6 +46,30 @@ public class SpanTest
         Assert.That(count, Is.EqualTo(8));
     }
 
+    [Test]
+    public void Replace_ShouldReplaceAllElements_GivenSpanOfInt32()
+    {
+        Span<int> span = stackalloc int[16] {1, 2, 3, 2, 5, 2, 7, 2, 9, 2, 11, 2, 13, 2, 15, 2};
+        span.Replace(2, 4);
+        Assert.That(span.ToArray(), Is.EqualTo(new[] {1, 4, 3, 4, 5, 4, 7, 4, 9, 4, 11, 4, 13, 4, 15, 4}));
+    }
+
+    [Test]
+    public void Replace_ShouldReplaceAllElements_GivenSpanOfChar()
+    {
+        Span<char> chars = stackalloc char[12] {'H', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', '!'};
+        chars.Replace('l', 'w');
+        CollectionAssert.AreEqual(chars.ToArray(), "Hewwo worwd!".ToCharArray());
+    }
+
+    [Test]
+    public void Replace_ShouldDoNothing_GivenSpanWithNoMatchingElements()
+    {
+        Span<int> span = stackalloc int[16] {1, 2, 3, 2, 5, 2, 7, 2, 9, 2, 11, 2, 13, 2, 15, 2};
+        span.Replace(4, 8);
+        Assert.That(span.ToArray(), Is.EqualTo(new[] {1, 2, 3, 2, 5, 2, 7, 2, 9, 2, 11, 2, 13, 2, 15, 2}));
+    }
+
     [Test]
     public void Split_OnEmptySpan_ShouldYieldNothing_UsingCharDelimiter_GivenReadOnlySpan()
     {
diff --git a/X10D/src/Collections/SpanExtensions.cs b/X10D/src/Collections/SpanExtensions.cs
index 78d6c8b..1aee61d 100644
--- a/X10D/src/Collections/SpanExtensions.cs
+++ b/X10D/src/Collections/SpanExtensions.cs
@@ -1,4 +1,9 @@
-namespace X10D.Collections;
+#if NET5_0_OR_GREATER
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+#endif
+
+namespace X10D.Collections;
 
 /// <summary>
 ///     Extension methods for <see cref="Span{T}" /> and <see cref="ReadOnlySpan{T}" />
@@ -53,6 +58,26 @@ public static class SpanExtensions
         return source;
     }
 
+    /// <summary>
+    ///     Replaces all occurrences of a specified element in a span of elements with another specified element.
+    /// </summary>
+    /// <param name="haystack">The source span.</param>
+    /// <param name="needle">The element to replace.</param>
+    /// <param name="replacement">The replacement element.</param>
+    /// <typeparam name="T">The type of elements in <paramref name="haystack" />.</typeparam>
+    public static void Replace<T>(this Span<T> haystack, T needle, T replacement) where T : struct
+    {
+        var comparer = EqualityComparer<T>.Default;
+
+        for (var index = 0; index < haystack.Length; index++)
+        {
+            if (comparer.Equals(haystack[index], needle))
+            {
+                haystack[index] = replacement;
+            }
+        }
+    }
+
     /// <summary>
     ///     Splits a span of elements into sub-spans based on a delimiting element.
     /// </summary>