Added EnumerateStringBuilder sample

Author: linkdotnet

EnumerateStringBuilder/EnumerateStringBuilder.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net7.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <PackageReference Include="BenchmarkDotNet" Version="0.13.2" />
+    </ItemGroup>
+
+</Project>

EnumerateStringBuilder/EnumerateStringBuilder.sln

@@ -0,0 +1,16 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "EnumerateStringBuilder", "EnumerateStringBuilder.csproj", "{733A44FC-57DB-4556-8A03-6B47566FA9F4}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{733A44FC-57DB-4556-8A03-6B47566FA9F4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{733A44FC-57DB-4556-8A03-6B47566FA9F4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{733A44FC-57DB-4556-8A03-6B47566FA9F4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{733A44FC-57DB-4556-8A03-6B47566FA9F4}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

EnumerateStringBuilder/Program.cs

@@ -0,0 +1,80 @@
+using System.Text;
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Running;
+
+BenchmarkRunner.Run<Benchmark>();
+
+[MemoryDiagnoser]
+public class Benchmark
+{
+    private StringBuilder _sb = default!;
+
+    [Params(10, 100, 1000)]
+    public int Chars { get; set; }
+
+    [GlobalSetup]
+    public void Setup() => _sb = new StringBuilder(new string('c', Chars));
+
+    [Benchmark(Baseline = true)]
+    public void EnumeratorViaToString()
+    {
+        foreach (var c in _sb.ToString()) _ = c;
+    }
+
+    [Benchmark]
+    public void EnumeratorViaExtension()
+    {
+        foreach (var c in _sb) _ = c;
+    }
+
+    [Benchmark]
+    public void IterateViaForLoop()
+    {
+        for (var i = 0; i < _sb.Length; i++)
+            _ = _sb[i];
+    }
+
+    [Benchmark]
+    public void ViaChunkEnumerator()
+    {
+        foreach (var chunk in _sb.GetChunks())
+        {
+            foreach (var c in chunk.Span)
+                _ = c;
+        }
+    }
+}
+
+public static class Extensions
+{
+    public static StringEnumerator GetEnumerator(this StringBuilder s) => new(s);
+}
+
+/// <summary>
+/// ref structs can't escape to the heap
+/// We do this to further optimize the runtime and allocations
+/// I know that mutable value types are evil, but normally this type
+/// is not handled by user-code, so it is fine
+/// </summary>
+public ref struct StringEnumerator
+{
+    private readonly StringBuilder _stringBuilder;
+    private int _index = -1;
+    public StringEnumerator(StringBuilder stringBuilder) => _stringBuilder = stringBuilder;
+
+    public bool MoveNext()
+    {
+        _index++;
+        return _index < _stringBuilder.Length;
+    }
+
+    /// <summary>
+    /// This is potentially dangerous as this is not always O(1)
+    /// The StringBuilder has chunks, which are at most 8000 bytes long
+    /// So having a string longer than 8000 bytes might have to access
+    /// the second chunk.
+    /// </summary>
+    public char Current => _stringBuilder[_index];
+
+    public void Dispose() => _index = -1;
+}

EnumerateStringBuilder/README.md

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+# How to enumerate through a StringBuilder
+
+Did you ever wonder how we can iterate through a `StringBuilder`? I mean, of course, we can just call `ToString` and use the returned string, but that means we materialize the whole thing without good reason. 
+
+We can also use a normal for-loop. But we can also find a completely different and probably dumber way!  And if you wonder: No, this is not something you do in your daily life, but by doing that thing, I can show some cool stuff C# and .NET offer.
+
+Found [here](https://steven-giesel.com/blogPost/5161909a-a223-4312-b939-996a0f97bf75)

README.md

@@ -4,6 +4,7 @@ Contains all of my examples from various blog posts. You can find a comprehensiv
 
 | BlogPost                                                                                 | Publish Date |
 | ---------------------------------------------------------------------------------------- | ------------ |
+| [How to enumerate through a StringBuilder](EnumerateStringBuilder/)                      | 03.12.2022   |
 | [Frozen collections in .NET 8](FrozenSetBenchmark/)                                      | 24.11.2022   |
 | ["Use always a StringBuilder" - Internet myths](StringBuilderPerformance/)               | 20.11.2022   |
 | [Anonymous test data with AutoFixture](AutoFixtureXUnit/)                                | 19.11.2022   |