Added c'tor with initial buffer

Author: linkdotnet

CHANGELOG.md

@@ -6,6 +6,9 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 
 ## [Unreleased]
 
+### Added
+ - `ValueStringBuilder` constructor can take initial buffer instead of creating it itself.
+
 ## [1.1.0] - 2022-04-16
 
 ### Added
@@ -87,4 +90,4 @@ This release brings extensions to the `ValueStringBuilder` API. For `v1.0` the `
 
 [1.0.0]: https://github.com/linkdotnet/StringBuilder/compare/0.9.5...1.0.0
 
-[0.9.5]: https://github.com/linkdotnet/StringBuilder/compare/0.9.4...0.9.5
+[0.9.5]: https://github.com/linkdotnet/StringBuilder/compare/0.9.4...0.9.5

src/LinkDotNet.StringBuilder/ValueStringBuilder.cs

@@ -25,6 +25,16 @@ public ValueStringBuilder()
         buffer = new char[32];
     }
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ValueStringBuilder"/> struct.
+    /// </summary>
+    /// <param name="initialBuffer">Initial buffer for the string builder to begin with.</param>
+    public ValueStringBuilder(Span<char> initialBuffer)
+    {
+        bufferPosition = 0;
+        buffer = initialBuffer;
+    }
+
     /// <summary>
     /// Gets the current length of the represented string.
     /// </summary>

tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs

@@ -323,4 +323,15 @@ public void ShouldReturnIfStringIsPresent(string word, bool expected)
 
         index.Should().Be(expected);
     }
+
+    [Fact]
+    public void ShouldUseInitialBuffer()
+    {
+        Span<char> buffer = stackalloc char[16];
+        var builder = new ValueStringBuilder(buffer);
+
+        builder.Append("Hello");
+
+        builder.ToString().Should().Be("Hello");
+    }
 }