feat: introduce ReadOnlySpan overloads for Concat and AppendJoin methods to enhance performance

Author: linkdotnet

CHANGELOG.md

@@ -6,6 +6,11 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 
 ## [Unreleased]
 
+This is the `v3` major release. The API is almost the same as in `v2` - there is only a slight change in the `Concat` static helper method to reflect a less-boxed API.
+
+### Changed
+- `ValueStringBuilder.Concat` uses `params ReadOnlySpan<T>` to reduce boxing and improve performance.
+
 ## [2.4.1] - 2025-03-25
 
 ### Changed

src/LinkDotNet.StringBuilder/LinkDotNet.StringBuilder.csproj

@@ -42,7 +42,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-      <PackageReference Include="Meziantou.Analyzer" Version="2.0.199">
+      <PackageReference Include="Meziantou.Analyzer" Version="2.0.200">
         <PrivateAssets>all</PrivateAssets>
         <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       </PackageReference>

src/LinkDotNet.StringBuilder/ValueStringBuilder.AppendJoin.cs

@@ -14,6 +14,24 @@ public ref partial struct ValueStringBuilder
     public void AppendJoin(ReadOnlySpan<char> separator, IEnumerable<string?> values)
         => AppendJoinInternalString(separator, values);
 
+    /// <summary>
+    /// Concatenates and appends all values with the given separator between each entry at the end of the string.
+    /// </summary>
+    /// <param name="separator">String used as separator between the entries.</param>
+    /// <param name="values">Enumerable of strings to be concatenated.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AppendJoin(ReadOnlySpan<char> separator, ReadOnlySpan<string?> values)
+        => AppendJoinInternalString(separator, values);
+
+    /// <summary>
+    /// Concatenates and appends all values with the given separator between each entry at the end of the string.
+    /// </summary>
+    /// <param name="separator">Character used as separator between the entries.</param>
+    /// <param name="values">Enumerable of strings to be concatenated.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AppendJoin(char separator, ReadOnlySpan<string?> values)
+        => AppendJoinInternalChar(separator, values);
+
     /// <summary>
     /// Concatenates and appends all values with the given separator between each entry at the end of the string.
     /// </summary>
@@ -42,6 +60,16 @@ public void AppendJoin(Rune separator, IEnumerable<string?> values)
     public void AppendJoin<T>(ReadOnlySpan<char> separator, IEnumerable<T> values)
         => AppendJoinInternalString(separator, values);
 
+    /// <summary>
+    /// Concatenates and appends all values with the given separator between each entry at the end of the string.
+    /// </summary>
+    /// <param name="separator">String used as separator between the entries.</param>
+    /// <param name="values">Enumerable to be concatenated.</param>
+    /// <typeparam name="T">Type of the given enumerable.</typeparam>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AppendJoin<T>(ReadOnlySpan<char> separator, ReadOnlySpan<T> values)
+        => AppendJoinInternalString(separator, values);
+
     /// <summary>
     /// Concatenates and appends all values with the given separator between each entry at the end of the string.
     /// </summary>
@@ -52,6 +80,16 @@ public void AppendJoin<T>(ReadOnlySpan<char> separator, IEnumerable<T> values)
     public void AppendJoin<T>(char separator, IEnumerable<T> values)
         => AppendJoinInternalChar(separator, values);
 
+    /// <summary>
+    /// Concatenates and appends all values with the given separator between each entry at the end of the string.
+    /// </summary>
+    /// <param name="separator">Character used as separator between the entries.</param>
+    /// <param name="values">Enumerable to be concatenated.</param>
+    /// <typeparam name="T">Type of the given enumerable.</typeparam>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public void AppendJoin<T>(char separator, ReadOnlySpan<T> values)
+        => AppendJoinInternalChar(separator, values);
+
     /// <summary>
     /// Concatenates and appends all values with the given separator between each entry at the end of the string.
     /// </summary>
@@ -85,6 +123,23 @@ private void AppendJoinInternalString<T>(ReadOnlySpan<char> separator, IEnumerab
         }
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private void AppendJoinInternalString<T>(ReadOnlySpan<char> separator, ReadOnlySpan<T> values)
+    {
+        if (values.Length == 0)
+        {
+            return;
+        }
+
+        AppendInternal(values[0]);
+
+        for (var i = 1; i < values.Length; i++)
+        {
+            Append(separator);
+            AppendInternal(values[i]);
+        }
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private void AppendJoinInternalChar<T>(char separator, IEnumerable<T> values)
     {
@@ -108,6 +163,23 @@ private void AppendJoinInternalChar<T>(char separator, IEnumerable<T> values)
         }
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private void AppendJoinInternalChar<T>(char separator, ReadOnlySpan<T> values)
+    {
+        if (values.Length == 0)
+        {
+            return;
+        }
+
+        AppendInternal(values[0]);
+
+        for (var i = 1; i < values.Length; i++)
+        {
+            Append(separator);
+            AppendInternal(values[i]);
+        }
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private void AppendJoinInternalRune<T>(Rune separator, IEnumerable<T> values)
     {

src/LinkDotNet.StringBuilder/ValueStringBuilder.Concat.Helper.cs

@@ -11,9 +11,9 @@ public ref partial struct ValueStringBuilder
     /// <typeparam name="T">Any given type, which can be translated to <see cref="string"/>.</typeparam>
     /// <returns>Concatenated string or an empty string if <paramref name="values"/> is empty.</returns>
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static string Concat<T>(params T[] values)
+    public static string Concat<T>(params ReadOnlySpan<T> values)
     {
-        if (values is null || values.Length == 0)
+        if (values.Length == 0)
         {
             return string.Empty;
         }

tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs

@@ -437,7 +437,7 @@ public void ConcatArbitraryValues()
     [Fact]
     public void ShouldReturnEmptyStringIfEmptyArray()
     {
-        var result = ValueStringBuilder.Concat(Array.Empty<string>());
+        var result = ValueStringBuilder.Concat<string>(Array.Empty<string>());
 
         result.ShouldBe(string.Empty);
     }
@@ -467,7 +467,7 @@ public void ConcatShouldHandleNullValues()
     {
         string[]? array = null;
 
-        ValueStringBuilder.Concat(array!).ShouldBe(string.Empty);
+        ValueStringBuilder.Concat<string>(array!).ShouldBe(string.Empty);
     }
 
     [Fact]