From 23e07b65b89b1302ebef45710c571fdbfe4d86d3 Mon Sep 17 00:00:00 2001
From: Oliver Booth <me@olivr.me>
Date: Thu, 12 May 2022 13:52:04 +0100
Subject: [PATCH] Add [ReadOnly]Span<T>.Count(Predicate<T>)

---
 CHANGELOG.md                             |  2 ++
 X10D.Tests/src/Linq/ReadOnlySpanTests.cs | 24 +++++++++++++++
 X10D.Tests/src/Linq/SpanTests.cs         | 24 +++++++++++++++
 X10D/src/Linq/ReadOnlySpanExtensions.cs  | 39 ++++++++++++++++++++++++
 X10D/src/Linq/SpanExtensions.cs          | 39 ++++++++++++++++++++++++
 5 files changed, 128 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3e227e0..ac2db5b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,7 +15,9 @@
 - X10D: Added `IEnumerable<T>.DisposeAll()`
 - X10D: Added `IEnumerable<T>.DisposeAllAsync()`
 - X10D: Added `char.IsEmoji`
+- X10D: Added `ReadOnlySpan<T>.Count(Predicate<T>)`
 - X10D: Added `Rune.IsEmoji`
+- X10D: Added `Span<T>.Count(Predicate<T>)`
 - X10D: Added `string.IsEmoji`
 - X10D: Added `Vector2.WithX()`
 - X10D: Added `Vector2.WithY()`
diff --git a/X10D.Tests/src/Linq/ReadOnlySpanTests.cs b/X10D.Tests/src/Linq/ReadOnlySpanTests.cs
index e33f5cd..4f2cbd9 100644
--- a/X10D.Tests/src/Linq/ReadOnlySpanTests.cs
+++ b/X10D.Tests/src/Linq/ReadOnlySpanTests.cs
@@ -55,4 +55,28 @@ public class ReadOnlySpanTests
             return span.Any(null!);
         });
     }
+
+    [TestMethod]
+    public void Count_ShouldReturn0_GivenEmptySpan()
+    {
+        var span = new ReadOnlySpan<int>();
+        Assert.AreEqual(0, span.Count(i => i % 2 == 0));
+    }
+
+    [TestMethod]
+    public void Count_ShouldReturn5_ForEvenNumbers_GivenNumbers1To10()
+    {
+        var span = new ReadOnlySpan<int>(new[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10});
+        Assert.AreEqual(5, span.Count(i => i % 2 == 0));
+    }
+
+    [TestMethod]
+    public void Count_ShouldThrow_GivenNullPredicate()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() =>
+        {
+            var span = new ReadOnlySpan<int>();
+            return span.Count(null!);
+        });
+    }
 }
diff --git a/X10D.Tests/src/Linq/SpanTests.cs b/X10D.Tests/src/Linq/SpanTests.cs
index 98c5fe3..60882f4 100644
--- a/X10D.Tests/src/Linq/SpanTests.cs
+++ b/X10D.Tests/src/Linq/SpanTests.cs
@@ -55,4 +55,28 @@ public class SpanTests
             return span.Any(null!);
         });
     }
+
+    [TestMethod]
+    public void Count_ShouldReturn0_GivenEmptySpan()
+    {
+        var span = new Span<int>();
+        Assert.AreEqual(0, span.Count(i => i % 2 == 0));
+    }
+
+    [TestMethod]
+    public void Count_ShouldReturn5_ForEvenNumbers_GivenNumbers1To10()
+    {
+        var span = new Span<int>(new[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10});
+        Assert.AreEqual(5, span.Count(i => i % 2 == 0));
+    }
+
+    [TestMethod]
+    public void Count_ShouldThrow_GivenNullPredicate()
+    {
+        Assert.ThrowsException<ArgumentNullException>(() =>
+        {
+            var span = new Span<int>();
+            return span.Count(null!);
+        });
+    }
 }
diff --git a/X10D/src/Linq/ReadOnlySpanExtensions.cs b/X10D/src/Linq/ReadOnlySpanExtensions.cs
index 8b10261..bf0d1d3 100644
--- a/X10D/src/Linq/ReadOnlySpanExtensions.cs
+++ b/X10D/src/Linq/ReadOnlySpanExtensions.cs
@@ -84,4 +84,43 @@ public static class ReadOnlySpanExtensions
 
         return false;
     }
+
+    /// <summary>
+    ///     Returns a number that represents how many elements in the specified sequence satisfy a condition.
+    /// </summary>
+    /// <param name="source">A <see cref="ReadOnlySpan{T}" /> that contains elements to be tested and counted.</param>
+    /// <param name="predicate">A function to test each element for a condition.</param>
+    /// <typeparam name="TSource">The type of the elements in <paramref name="source" />.</typeparam>
+    /// <returns>
+    ///     A number that represents how many elements in the sequence satisfy the condition in the predicate function.
+    /// </returns>
+    /// <exception cref="ArgumentNullException"><paramref name="predicate" /> is <see langword="null" />.</exception>
+    public static int Count<TSource>(this ReadOnlySpan<TSource> source, Predicate<TSource> predicate)
+    {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(predicate);
+#else
+        if (predicate is null)
+        {
+            throw new ArgumentNullException(nameof(predicate));
+        }
+#endif
+
+        if (source.IsEmpty)
+        {
+            return 0;
+        }
+
+        var count = 0;
+
+        foreach (TSource item in source)
+        {
+            if (predicate(item))
+            {
+                count++;
+            }
+        }
+
+        return count;
+    }
 }
diff --git a/X10D/src/Linq/SpanExtensions.cs b/X10D/src/Linq/SpanExtensions.cs
index d5a208a..ce2e3f3 100644
--- a/X10D/src/Linq/SpanExtensions.cs
+++ b/X10D/src/Linq/SpanExtensions.cs
@@ -84,4 +84,43 @@ public static class SpanExtensions
 
         return false;
     }
+
+    /// <summary>
+    ///     Returns a number that represents how many elements in the specified sequence satisfy a condition.
+    /// </summary>
+    /// <param name="source">A <see cref="Span{T}" /> that contains elements to be tested and counted.</param>
+    /// <param name="predicate">A function to test each element for a condition.</param>
+    /// <typeparam name="TSource">The type of the elements in <paramref name="source" />.</typeparam>
+    /// <returns>
+    ///     A number that represents how many elements in the sequence satisfy the condition in the predicate function.
+    /// </returns>
+    /// <exception cref="ArgumentNullException"><paramref name="predicate" /> is <see langword="null" />.</exception>
+    public static int Count<TSource>(this Span<TSource> source, Predicate<TSource> predicate)
+    {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(predicate);
+#else
+        if (predicate is null)
+        {
+            throw new ArgumentNullException(nameof(predicate));
+        }
+#endif
+
+        if (source.IsEmpty)
+        {
+            return 0;
+        }
+
+        var count = 0;
+
+        foreach (TSource item in source)
+        {
+            if (predicate(item))
+            {
+                count++;
+            }
+        }
+
+        return count;
+    }
 }