Merge 964d105f92 into 5ff7b68b37

.github/workflows/sonarcloud.yml

@@ -44,6 +44,11 @@ jobs:
           New-Item -Path .\.sonar\scanner -ItemType Directory
           dotnet tool update dotnet-sonarscanner --tool-path .\.sonar\scanner
 
+      - name: Install dotCover
+        shell: powershell
+        run: |
+          dotnet tool install --global JetBrains.dotCover.GlobalTool
+
       - name: Build and analyze
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}  # Needed to get PR information, if any

CHANGELOG.md

@@ -26,6 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - X10D: Added `string.ConcatIf`.
 - X10D: Added `string.MDBold`, `string.MDCode`, `string.MDCodeBlock([string])`, `string.MDHeading(int)`,
 `string.MDItalic`, `string.MDLink`, `string.MDStrikeOut`, and `string.MDUnderline` for Markdown formatting.
+- X10D: Added Span overloads which complement `char.Repeat` and `string.Repeat`.
 - X10D.Unity: Added `RaycastHit.GetComponent` and `RaycastHit.TryGetComponent`.
 - X10D.Unity: Added `DebugUtility.DrawFunction`, and `DebugUtility.DrawUnjoinedPolyhedron` on which it relies.
 
@@ -41,6 +42,7 @@ BigEndian/LittleEndian methods.
 - X10D: `Stream.GetHash<>` and `Stream.TryWriteHash<>` now throw ArgumentException in lieu of
 TypeInitializationException.
 - X10D: `char.IsEmoji` no longer allocates for .NET 7.
+- X10D: `string.Repeat` is now more efficient.
 
 ### Removed
 

Directory.Build.props

@@ -21,7 +21,7 @@
         <PackageIconUrl/>
         <PackageTags>dotnet extension-methods</PackageTags>
         <PackageReadmeFile>README.md</PackageReadmeFile>
-        <PackageReleaseNotes>$([System.IO.File]::ReadAllText("$(SolutionDir)/CHANGELOG.md"))</PackageReleaseNotes>
+        <PackageReleaseNotes>See CHANGELOG.md for a full list of changes.</PackageReleaseNotes>
         <CodeAnalysisTreatWarningsAsErrors>true</CodeAnalysisTreatWarningsAsErrors>
     </PropertyGroup>
 

X10D.Tests/src/Text/CharSpanTests.cs

@@ -60,4 +60,60 @@ internal class CharSpanTests
         Assert.That(string.Empty.AsSpan().CountSubstring('\0'), Is.Zero);
         Assert.That(string.Empty.AsSpan().CountSubstring(string.Empty.AsSpan(), StringComparison.OrdinalIgnoreCase), Is.Zero);
     }
+
+    [Test]
+    public void Repeat_ShouldNotManipulateSpan_GivenCount0()
+    {
+        Span<char> destination = new char[11];
+        "Hello world".AsSpan().CopyTo(destination);
+
+        "a".AsSpan().Repeat(0, destination);
+        Assert.That(destination.ToString(), Is.EqualTo("Hello world"));
+    }
+
+    [Test]
+    public void Repeat_ShouldReturnItself_GivenCount1()
+    {
+        string repeated = "a".AsSpan().Repeat(1);
+        Assert.That(repeated, Has.Length.EqualTo(1));
+        Assert.That(repeated, Is.EqualTo("a"));
+    }
+
+    [Test]
+    public void Repeat_ShouldPopulateSpan_GivenValidSpan()
+    {
+        const string expected = "aaaaaaaaaa";
+        Span<char> destination = new char[10];
+        "a".AsSpan().Repeat(10, destination);
+
+        Assert.That(destination.ToString(), Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void Repeat_ShouldReturnEmptyString_GivenCount0()
+    {
+        Assert.That("a".AsSpan().Repeat(0), Is.EqualTo(string.Empty));
+    }
+
+    [Test]
+    public void Repeat_ShouldReturnRepeatedString_GivenSpan()
+    {
+        const string expected = "aaaaaaaaaa";
+        string actual = "a".AsSpan().Repeat(10);
+
+        Assert.That(actual, Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void Repeat_ShouldThrowArgumentException_GivenSmallSpan()
+    {
+        Assert.Throws<ArgumentException>(() => "a".AsSpan().Repeat(10, Span<char>.Empty));
+    }
+
+    [Test]
+    public void Repeat_ShouldThrowArgumentOutOfRangeException_GivenNegativeCount()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => _ = "a".AsSpan().Repeat(-1));
+        Assert.Throws<ArgumentOutOfRangeException>(() => "a".AsSpan().Repeat(-1, Span<char>.Empty));
+    }
 }

X10D.Tests/src/Text/CharTests.cs

@@ -28,6 +28,25 @@ internal class CharTests
         }
     }
 
+    [Test]
+    public void Repeat_ShouldPopulateSpanWithRepeatedCharacter_GivenValidCount()
+    {
+        const string expected = "aaaaaaaaaa";
+        Span<char> destination = new char[10];
+        'a'.Repeat(10, destination);
+
+        Assert.That(destination.ToString(), Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void Repeat_ShouldOnlyWriteOneCharToSpan_GivenCount1()
+    {
+        Span<char> destination = new char[10];
+        'a'.Repeat(1, destination);
+
+        Assert.That(destination.ToString(), Is.EqualTo("a\0\0\0\0\0\0\0\0\0"));
+    }
+
     [Test]
     public void Repeat_ShouldReturnRepeatedCharacter_GivenValidCount()
     {
@@ -51,9 +70,34 @@ internal class CharTests
         Assert.That('a'.Repeat(0), Is.EqualTo(string.Empty));
     }
 
+    [Test]
+    public void Repeat_ShouldNotManipulateSpan_GivenCount0()
+    {
+        Span<char> destination = new char[10];
+        destination.Fill(' ');
+        'a'.Repeat(0, destination);
+
+        const string expected = "          ";
+        Assert.That(destination.ToString(), Is.EqualTo(expected));
+    }
+
     [Test]
     public void Repeat_ShouldThrowArgumentOutOfRangeException_GivenNegativeCount()
     {
-        Assert.Throws<ArgumentOutOfRangeException>(() => _ = 'a'.Repeat(-1));
+        Assert.Multiple(() =>
+        {
+            Assert.Throws<ArgumentOutOfRangeException>(() => _ = 'a'.Repeat(-1));
+            Assert.Throws<ArgumentOutOfRangeException>(() => 'a'.Repeat(-1, Span<char>.Empty));
+        });
+    }
+
+    [Test]
+    public void Repeat_ShouldThrowArgumentException_GivenSmallSpan()
+    {
+        Assert.Throws<ArgumentException>(() =>
+        {
+            var destination = Span<char>.Empty;
+            'a'.Repeat(1, destination);
+        });
     }
 }

X10D.Tests/src/Text/MarkdownTests.cs

@@ -105,6 +105,46 @@ internal class MarkdownTests
         Assert.That("Hello, world!".MDItalic(true), Is.EqualTo("_Hello, world!_"));
     }
 
+    [Test]
+    public void MDLink_ShouldThrowArgumentNullException_GivenNullUrl()
+    {
+        Assert.Multiple(() =>
+        {
+            Assert.Throws<ArgumentNullException>(() => "".MDLink((string)null!));
+            Assert.Throws<ArgumentNullException>(() => "".MDLink((Uri)null!));
+            Assert.Throws<ArgumentNullException>(() => ((Uri)null!).MDLink("Hello, world!"));
+        });
+    }
+
+    [Test]
+    public void MDLink_ShouldReturnUrlOnly_GivenNullOrEmptyLabel()
+    {
+        const string url = "https://example.com/";
+        Assert.Multiple(() =>
+        {
+            Assert.That(((string)null!).MDLink(url), Is.EqualTo(url));
+            Assert.That(string.Empty.MDLink(url), Is.EqualTo(url));
+
+            Assert.That(new Uri(url).MDLink(null), Is.EqualTo(url));
+            Assert.That(new Uri(url).MDLink(string.Empty), Is.EqualTo(url));
+        });
+    }
+
+    [Test]
+    public void MDLink_ShouldReturnFormattedLink_GivenValidLabelAndUrl()
+    {
+        const string url = "https://example.com/";
+        const string label = "Hello, world!";
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(label.MDLink(url), Is.EqualTo($"[{label}]({url})"));
+            Assert.That(label.MDLink(new Uri(url)), Is.EqualTo($"[{label}]({url})"));
+
+            Assert.That(new Uri(url).MDLink(label), Is.EqualTo($"[{label}]({url})"));
+        });
+    }
+
     [Test]
     public void MDStrikeOut_ShouldThrowArgumentNullException_GivenNull()
     {

X10D.Tests/src/Text/StringTests.cs

@@ -164,7 +164,9 @@ internal class StringTests
         Assert.Multiple(() =>
         {
             Assert.That("Hello World".CountSubstring('E'), Is.Zero);
+#pragma warning disable CA1307
             Assert.That("Hello World".CountSubstring("E"), Is.Zero);
+#pragma warning restore CA1307
             Assert.That("Hello World".CountSubstring("E", StringComparison.OrdinalIgnoreCase), Is.EqualTo(1));
         });
     }
@@ -175,7 +177,9 @@ internal class StringTests
         Assert.Multiple(() =>
         {
             Assert.That("Hello World".CountSubstring('z'), Is.Zero);
+#pragma warning disable CA1307
             Assert.That("Hello World".CountSubstring("z"), Is.Zero);
+#pragma warning restore CA1307
             Assert.That("Hello World".CountSubstring("z", StringComparison.OrdinalIgnoreCase), Is.Zero);
         });
     }
@@ -186,7 +190,9 @@ internal class StringTests
         Assert.Multiple(() =>
         {
             Assert.That("Hello World".CountSubstring('e'), Is.EqualTo(1));
+#pragma warning disable CA1307
             Assert.That("Hello World".CountSubstring("e"), Is.EqualTo(1));
+#pragma warning restore CA1307
             Assert.That("Hello World".CountSubstring("e", StringComparison.OrdinalIgnoreCase), Is.EqualTo(1));
         });
     }
@@ -197,7 +203,9 @@ internal class StringTests
         Assert.Multiple(() =>
         {
             Assert.That(string.Empty.CountSubstring('\0'), Is.Zero);
+#pragma warning disable CA1307
             Assert.That(string.Empty.CountSubstring(string.Empty), Is.Zero);
+#pragma warning restore CA1307
             Assert.That(string.Empty.CountSubstring(string.Empty, StringComparison.OrdinalIgnoreCase), Is.Zero);
         });
     }
@@ -207,7 +215,9 @@ internal class StringTests
     {
         string value = null!;
         Assert.Throws<ArgumentNullException>(() => value.CountSubstring('\0'));
+#pragma warning disable CA1307
         Assert.Throws<ArgumentNullException>(() => value.CountSubstring(string.Empty));
+#pragma warning restore CA1307
         Assert.Throws<ArgumentNullException>(() => value.CountSubstring(string.Empty, StringComparison.OrdinalIgnoreCase));
     }
 
@@ -217,7 +227,10 @@ internal class StringTests
         const string value = "Hello Worl";
         const char substring = 'd';
 
+#pragma warning disable CA1307
         Assert.That(value.EnsureEndsWith(substring), Is.EqualTo("Hello World"));
+#pragma warning restore CA1307
+        Assert.That(value.EnsureEndsWith(substring, StringComparison.Ordinal), Is.EqualTo("Hello World"));
     }
 
     [Test]
@@ -226,7 +239,10 @@ internal class StringTests
         const string value = "A";
         const char substring = 'A';
 
+#pragma warning disable CA1307
         Assert.That(value.EnsureEndsWith(substring), Is.EqualTo(value));
+#pragma warning restore CA1307
+        Assert.That(value.EnsureEndsWith(substring, StringComparison.Ordinal), Is.EqualTo(value));
     }
 
     [Test]
@@ -235,7 +251,10 @@ internal class StringTests
         const string value = "B";
         const char substring = 'A';
 
+#pragma warning disable CA1307
         Assert.That(value.EnsureStartsWith(substring), Is.EqualTo("AB"));
+#pragma warning restore CA1307
+        Assert.That(value.EnsureStartsWith(substring, StringComparison.Ordinal), Is.EqualTo("AB"));
     }
 
     [Test]
@@ -244,7 +263,10 @@ internal class StringTests
         const string value = "A";
         const char substring = 'A';
 
+#pragma warning disable CA1307
         Assert.That(value.EnsureStartsWith(substring), Is.EqualTo(value));
+#pragma warning restore CA1307
+        Assert.That(value.EnsureStartsWith(substring, StringComparison.Ordinal), Is.EqualTo(value));
     }
 
     [Test]
@@ -253,7 +275,10 @@ internal class StringTests
         const string value = "Hello ";
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(value.EnsureEndsWith(substring), Is.EqualTo("Hello World"));
+#pragma warning restore CA1307
+        Assert.That(value.EnsureEndsWith(substring, StringComparison.Ordinal), Is.EqualTo("Hello World"));
     }
 
     [Test]
@@ -261,7 +286,10 @@ internal class StringTests
     {
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(substring.EnsureEndsWith(substring), Is.EqualTo(substring));
+#pragma warning restore CA1307
+        Assert.That(substring.EnsureEndsWith(substring, StringComparison.Ordinal), Is.EqualTo(substring));
     }
 
     [Test]
@@ -269,7 +297,10 @@ internal class StringTests
     {
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(string.Empty.EnsureEndsWith(substring), Is.EqualTo(substring));
+#pragma warning restore CA1307
+        Assert.That(string.Empty.EnsureEndsWith(substring, StringComparison.Ordinal), Is.EqualTo(substring));
     }
 
     [Test]
@@ -277,7 +308,10 @@ internal class StringTests
     {
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(substring.EnsureEndsWith(string.Empty), Is.EqualTo(substring));
+#pragma warning restore CA1307
+        Assert.That(substring.EnsureEndsWith(string.Empty, StringComparison.Ordinal), Is.EqualTo(substring));
     }
 
     [Test]
@@ -286,7 +320,10 @@ internal class StringTests
         const string value = "World";
         const string substring = "Hello ";
 
+#pragma warning disable CA1307
         Assert.That(value.EnsureStartsWith(substring), Is.EqualTo("Hello World"));
+#pragma warning restore CA1307
+        Assert.That(value.EnsureStartsWith(substring, StringComparison.Ordinal), Is.EqualTo("Hello World"));
     }
 
     [Test]
@@ -294,7 +331,10 @@ internal class StringTests
     {
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(substring.EnsureStartsWith(substring), Is.EqualTo(substring));
+#pragma warning restore CA1307
+        Assert.That(substring.EnsureStartsWith(substring, StringComparison.Ordinal), Is.EqualTo(substring));
     }
 
     [Test]
@@ -302,7 +342,10 @@ internal class StringTests
     {
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(string.Empty.EnsureStartsWith(substring), Is.EqualTo(substring));
+#pragma warning restore CA1307
+        Assert.That(string.Empty.EnsureStartsWith(substring, StringComparison.Ordinal), Is.EqualTo(substring));
     }
 
     [Test]
@@ -310,7 +353,10 @@ internal class StringTests
     {
         const string substring = "World";
 
+#pragma warning disable CA1307
         Assert.That(substring.EnsureStartsWith(string.Empty), Is.EqualTo(substring));
+#pragma warning restore CA1307
+        Assert.That(substring.EnsureStartsWith(string.Empty, StringComparison.Ordinal), Is.EqualTo(substring));
     }
 
     [Test]
@@ -393,7 +439,7 @@ internal class StringTests
     [Test]
     public void GetBytes_ShouldReturnUtf8Bytes_GivenHelloWorld()
     {
-        var expected = new byte[] {0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x57, 0x6F, 0x72, 0x6C, 0x64};
+        var expected = new byte[] { 0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x57, 0x6F, 0x72, 0x6C, 0x64 };
         byte[] actual = "Hello World".GetBytes();
 
         CollectionAssert.AreEqual(expected, actual);
@@ -402,7 +448,7 @@ internal class StringTests
     [Test]
     public void GetBytes_ShouldReturnAsciiBytes_GivenHelloWorld()
     {
-        var expected = new byte[] {0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x57, 0x6F, 0x72, 0x6C, 0x64};
+        var expected = new byte[] { 0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x57, 0x6F, 0x72, 0x6C, 0x64 };
         byte[] actual = "Hello World".GetBytes(Encoding.ASCII);
 
         CollectionAssert.AreEqual(expected, actual);
@@ -444,14 +490,16 @@ internal class StringTests
     public void IsEmoji_ShouldReturnTrue_GivenMultiByteEmoji()
     {
         string[] regionalIndicatorCodes = Enumerable.Range(0, 26)
-            .Select(i => Encoding.Unicode.GetString(new byte[] {0x3C, 0xD8, (byte)(0xE6 + i), 0xDD}))
+            .Select(i => Encoding.Unicode.GetString(new byte[] { 0x3C, 0xD8, (byte)(0xE6 + i), 0xDD }))
             .ToArray();
 
         for (var i = 0; i < 26; i++)
-        for (var j = 0; j < 26; j++)
         {
-            string flag = (regionalIndicatorCodes[i] + regionalIndicatorCodes[j]);
+            for (var j = 0; j < 26; j++)
-            Assert.That(flag.IsEmoji());
+            {
+                string flag = (regionalIndicatorCodes[i] + regionalIndicatorCodes[j]);
+                Assert.That(flag.IsEmoji());
+            }
         }
     }
 
@@ -696,7 +744,7 @@ internal class StringTests
     [Test]
     public void Randomize_ShouldThrow_GivenNegativeLength()
     {
-        Assert.Throws<ArgumentOutOfRangeException>(() => string.Empty.Randomize(-1));
+        Assert.Throws<ArgumentOutOfRangeException>(() => _ = string.Empty.Randomize(-1));
     }
 
     [Test]
@@ -714,25 +762,62 @@ internal class StringTests
         Assert.That("a".Repeat(0), Is.EqualTo(string.Empty));
     }
 
+    [Test]
+    public void Repeat_ShouldNotManipulateSpan_GivenCount0()
+    {
+        Span<char> destination = new char[11];
+        "Hello world".AsSpan().CopyTo(destination);
+
+        "a".Repeat(0, destination);
+        Assert.That(destination.ToString(), Is.EqualTo("Hello world"));
+    }
+
     [Test]
     public void Repeat_ShouldReturnItself_GivenCount1()
     {
         string repeated = "a".Repeat(1);
-        Assert.That(repeated.Length, Is.EqualTo(1));
+        Assert.That(repeated, Has.Length.EqualTo(1));
         Assert.That(repeated, Is.EqualTo("a"));
     }
 
     [Test]
-    public void Repeat_ShouldThrow_GivenNegativeCount()
+    public void Repeat_ShouldThrowArgumentException_GivenSmallSpan()
     {
-        Assert.Throws<ArgumentOutOfRangeException>(() => _ = "a".Repeat(-1));
+        Assert.Throws<ArgumentException>(() => "a".Repeat(10, Span<char>.Empty));
     }
 
     [Test]
-    public void Repeat_ShouldThrow_GivenNull()
+    public void Repeat_ShouldThrowArgumentOutOfRangeException_GivenNegativeCount()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => _ = "a".Repeat(-1));
+        Assert.Throws<ArgumentOutOfRangeException>(() => "a".Repeat(-1, Span<char>.Empty));
+    }
+
+    [Test]
+    public void Repeat_ShouldThrowArgumentNullException_GivenNull()
     {
         string value = null!;
         Assert.Throws<ArgumentNullException>(() => _ = value.Repeat(0));
+        Assert.Throws<ArgumentNullException>(() => value.Repeat(0, Span<char>.Empty));
+    }
+
+    [Test]
+    public void Repeat_ShouldPopulateSpanWithRepeatedCharacter_GivenValidCount()
+    {
+        const string expected = "aaaaaaaaaa";
+        Span<char> destination = new char[10];
+        "a".Repeat(10, destination);
+
+        Assert.That(destination.ToString(), Is.EqualTo(expected));
+    }
+
+    [Test]
+    public void Repeat_ShouldOnlyWriteOneCharToSpan_GivenCount1()
+    {
+        Span<char> destination = new char[10];
+        "a".Repeat(1, destination);
+
+        Assert.That(destination.ToString(), Is.EqualTo("a\0\0\0\0\0\0\0\0\0"));
     }
 
     [Test]
@@ -751,7 +836,7 @@ internal class StringTests
     }
 
     [Test]
-    public void Reverse_ShouldThrow_GivenNull()
+    public void Reverse_ShouldThrowArgumentNullException_GivenNull()
     {
         string value = null!;
         Assert.Throws<ArgumentNullException>(() => _ = value.Reverse());
@@ -769,7 +854,7 @@ internal class StringTests
     }
 
     [Test]
-    public void Shuffled_ShouldThrow_GivenNull()
+    public void Shuffled_ShouldThrowArgumentNullException_GivenNull()
     {
         string value = null!;
         Assert.Throws<ArgumentNullException>(() => _ = value.Shuffled());
@@ -803,7 +888,7 @@ internal class StringTests
     }
 
     [Test]
-    public void Split_ShouldThrow_GivenNullString()
+    public void Split_ShouldThrowArgumentNullException_GivenNullString()
     {
         string value = null!;
 
@@ -878,7 +963,7 @@ internal class StringTests
     [Test]
     public void StartsWithAny_ShouldThrowArgumentNullException_GivenANullValue()
     {
-        var values = new[] {"Hello", null!, "World"};
+        var values = new[] { "Hello", null!, "World" };
         Assert.Throws<ArgumentNullException>(() => "Foobar".StartsWithAny(values));
         Assert.Throws<ArgumentNullException>(() => "Foobar".StartsWithAny(StringComparison.Ordinal, values));
     }

X10D/src/Text/CharExtensions.cs

@@ -47,4 +47,34 @@ public static class CharExtensions
             _ => new string(value, count)
         };
     }
+
+    /// <summary>
+    ///     Writes a character to a span of characters, repeated a specified number of times.
+    /// </summary>
+    /// <param name="value">The character to repeat.</param>
+    /// <param name="count">The number of times to repeat.</param>
+    /// <param name="destination">The span of characters into which the repeated characters will be written.</param>
+    [MethodImpl(CompilerResources.MethodImplOptions)]
+    public static void Repeat(this char value, int count, Span<char> destination)
+    {
+        if (count < 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
+        }
+
+        if (count == 0)
+        {
+            return;
+        }
+
+        if (destination.Length < count)
+        {
+            throw new ArgumentException(ExceptionMessages.DestinationSpanLengthTooShort, nameof(destination));
+        }
+
+        for (var i = 0; i < count; i++)
+        {
+            destination[i] = value;
+        }
+    }
 }

X10D/src/Text/CharSpanExtensions.cs

@@ -1,3 +1,8 @@
+using System.Diagnostics.Contracts;
+using System.Runtime.CompilerServices;
+using System.Text;
+using X10D.CompilerServices;
+
 namespace X10D.Text;
 
 /// <summary>
@@ -67,4 +72,73 @@ public static class CharSpanExtensions
 
         return count;
     }
+
+    /// <summary>
+    ///     Repeats a span of characters a specified number of times.
+    /// </summary>
+    /// <param name="value">The string to repeat.</param>
+    /// <param name="count">The repeat count.</param>
+    /// <returns>A string containing <paramref name="value" /> repeated <paramref name="count" /> times.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
+    /// <exception cref="ArgumentOutOfRangeException"><paramref name="count" /> is less than 0.</exception>
+    [Pure]
+    [MethodImpl(CompilerResources.MethodImplOptions)]
+    public static string Repeat(this ReadOnlySpan<char> value, int count)
+    {
+        switch (count)
+        {
+            case < 0:
+                throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
+
+            case 0:
+                return string.Empty;
+
+            case 1:
+                return value.ToString();
+        }
+
+        var builder = new StringBuilder(value.Length * count);
+
+        for (var i = 0; i < count; i++)
+        {
+            builder.Append(value);
+        }
+
+        return builder.ToString();
+    }
+
+    /// <summary>
+    ///     Repeats a span of character a specified number of times, writing the result to another span of characters.
+    /// </summary>
+    /// <param name="value">The span of characters to repeat.</param>
+    /// <param name="count">The repeat count.</param>
+    /// <param name="destination">The destination span to write to.</param>
+    /// <exception cref="ArgumentOutOfRangeException"><paramref name="count" /> is less than 0.</exception>
+    /// <exception cref="ArgumentException">
+    ///     <paramref name="destination" /> is too short to contain the repeated string.
+    /// </exception>
+    [MethodImpl(CompilerResources.MethodImplOptions)]
+    public static void Repeat(this ReadOnlySpan<char> value, int count, Span<char> destination)
+    {
+        if (count < 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
+        }
+
+        if (count == 0)
+        {
+            return;
+        }
+
+        if (destination.Length < value.Length * count)
+        {
+            throw new ArgumentException(ExceptionMessages.DestinationSpanLengthTooShort, nameof(destination));
+        }
+
+        for (var iteration = 0; iteration < count; iteration++)
+        {
+            Span<char> slice = destination.Slice(iteration * value.Length, value.Length);
+            value.CopyTo(slice);
+        }
+    }
 }

X10D/src/Text/StringExtensions.cs

@@ -932,14 +932,50 @@ public static class StringExtensions
                 return value;
         }
 
-        var builder = new StringBuilder(value.Length * count);
+        Span<char> destination = stackalloc char[value.Length * count];
+        value.Repeat(count, destination);
+        return new string(destination);
+    }
 
-        for (var i = 0; i < count; i++)
+    /// <summary>
+    ///     Repeats a string a specified number of times, writing the result to a span of characters.
+    /// </summary>
+    /// <param name="value">The string to repeat.</param>
+    /// <param name="count">The repeat count.</param>
+    /// <param name="destination">The destination span to write to.</param>
+    /// <exception cref="ArgumentNullException"><paramref name="value" /> is <see langword="null" />.</exception>
+    /// <exception cref="ArgumentOutOfRangeException"><paramref name="count" /> is less than 0.</exception>
+    /// <exception cref="ArgumentException">
+    ///     <paramref name="destination" /> is too short to contain the repeated string.
+    /// </exception>
+    [MethodImpl(CompilerResources.MethodImplOptions)]
+    public static void Repeat(this string value, int count, Span<char> destination)
+    {
+        if (value is null)
         {
-            builder.Append(value);
+            throw new ArgumentNullException(nameof(value));
         }
 
-        return builder.ToString();
+        if (count < 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(count), ExceptionMessages.CountMustBeGreaterThanOrEqualTo0);
+        }
+
+        if (count == 0)
+        {
+            return;
+        }
+
+        if (destination.Length < value.Length * count)
+        {
+            throw new ArgumentException(ExceptionMessages.DestinationSpanLengthTooShort, nameof(destination));
+        }
+
+        for (var iteration = 0; iteration < count; iteration++)
+        {
+            Span<char> slice = destination.Slice(iteration * value.Length, value.Length);
+            value.AsSpan().CopyTo(slice);
+        }
     }
 
     /// <summary>