Return pinnable reference

Author: linkdotnet

CHANGELOG.md

@@ -8,6 +8,7 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 
 ### Added
  - Added `Replace` methods which also tries to have the least amount of allocations.
+ - Added `GetPinnableReference` which allows to get the content via the `fixed` keyword.
 
 ## [0.9.2] - 2022-04-06
 

src/LinkDotNet.StringBuilder/ValueStringBuilder.cs

@@ -1,4 +1,5 @@
 using System.Buffers;
+using System.Runtime.InteropServices;
 
 namespace LinkDotNet.StringBuilder;
 
@@ -49,6 +50,24 @@ public ValueStringBuilder()
     /// <returns>The filled array as <see cref="ReadOnlySpan{T}"/>.</returns>
     public ReadOnlySpan<char> AsSpan() => buffer[..bufferPosition];
 
+    /// <summary>
+    /// Get a pinnable reference to the represented string from this builder.
+    /// The content after <see cref="Length"/> is not guaranteed to be null terminated.
+    /// </summary>
+    /// <returns>The pointer to the first instance of the string represented by this builder.</returns>
+    /// <remarks>
+    /// This method is used for use-cases where the user wants to use "fixed" calls like the following:
+    /// <code>
+    /// var stringBuilder = new ValueStringBuilder();
+    /// stringBuilder.Append("Hello World");
+    /// fixed (var* buffer = stringBuilder) { ... }
+    /// </code>
+    /// </remarks>
+    public ref char GetPinnableReference()
+    {
+        return ref MemoryMarshal.GetReference(buffer);
+    }
+
     /// <summary>
     /// Tries to copy the represented string into the given <see cref="Span{T}"/>.
     /// </summary>
@@ -105,6 +124,9 @@ public void Remove(int startIndex, int length)
     private void Grow(int capacity = 0)
     {
         var currentSize = buffer.Length;
+
+        // This could lead to the potential problem that an user sets the capacity smaller than the current length
+        // which would lead to a truncated string.
         var newSize = capacity > 0 ? capacity : currentSize * 2;
         var rented = ArrayPool<char>.Shared.Rent(newSize);
         buffer.CopyTo(rented);

tests/LinkDotNet.StringBuilder.UnitTests/LinkDotNet.StringBuilder.UnitTests.csproj

@@ -4,6 +4,7 @@
         <TargetFramework>net6.0</TargetFramework>
         <Nullable>enable</Nullable>
         <IsPackable>false</IsPackable>
+        <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     </PropertyGroup>
 
     <ItemGroup>

tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs

@@ -185,4 +185,18 @@ public void ShouldNotRemoveEntriesWhenLengthIsEqualToZero()
 
         stringBuilder.ToString().Should().Be("Hello");
     }
+
+    [Fact]
+    public unsafe void ShouldGetPinnableReference()
+    {
+        var stringBuilder = new ValueStringBuilder();
+        stringBuilder.Append("Hey");
+
+        fixed (char* c = stringBuilder)
+        {
+            c[0].Should().Be('H');
+            c[1].Should().Be('e');
+            c[2].Should().Be('y');
+        }
+    }
 }