From fdde1980cada77656e28fb75784282fdd47f908f Mon Sep 17 00:00:00 2001
From: Steven Giesel <stgiesel35@gmail.com>
Date: Thu, 8 Jun 2023 21:23:18 +0200
Subject: [PATCH] feat: Builder can be used in foreach loops

---
 CHANGELOG.md                                  |  4 ++
 .../ValueStringBuilder.Enumerator.cs          | 48 +++++++++++++++++++
 stylecop.analyzers.ruleset                    |  2 +
 .../ValueStringBuilderTests.cs                | 14 ++++++
 4 files changed, 68 insertions(+)
 create mode 100644 src/LinkDotNet.StringBuilder/ValueStringBuilder.Enumerator.cs

diff --git a/CHANGELOG.md b/CHANGELOG.md
index abb2f7a..478943c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 
 ## [Unreleased]
 
+### Added
+
+- Added custom enumerator to `ValueStringBuilder` so it can be used in `foreach` loops
+
 ## [1.17.0] - 2023-04-13
 
 ### Added
diff --git a/src/LinkDotNet.StringBuilder/ValueStringBuilder.Enumerator.cs b/src/LinkDotNet.StringBuilder/ValueStringBuilder.Enumerator.cs
new file mode 100644
index 0000000..08b829f
--- /dev/null
+++ b/src/LinkDotNet.StringBuilder/ValueStringBuilder.Enumerator.cs
@@ -0,0 +1,48 @@
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace LinkDotNet.StringBuilder;
+
+public ref partial struct ValueStringBuilder
+{
+    public readonly Enumerator GetEnumerator() => new(buffer[..bufferPosition]);
+
+    /// <summary>Enumerates the elements of a <see cref="Span{T}"/>.</summary>
+    [StructLayout(LayoutKind.Auto)]
+    public ref struct Enumerator
+    {
+        private readonly Span<char> span;
+        private int index;
+
+        /// <summary>Initializes a new instance of the <see cref="Enumerator"/> struct.</summary>
+        /// <param name="span">The span to enumerate.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal Enumerator(Span<char> span)
+        {
+            this.span = span;
+            index = -1;
+        }
+
+        /// <summary>Gets the element at the current position of the enumerator.</summary>
+        public ref char Current
+        {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get => ref span[index];
+        }
+
+        /// <summary>Advances the enumerator to the next element of the span.</summary>
+        /// <returns>True if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the span.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool MoveNext()
+        {
+            var nextIndex = index + 1;
+            if (nextIndex < span.Length)
+            {
+                index = nextIndex;
+                return true;
+            }
+
+            return false;
+        }
+    }
+}
\ No newline at end of file
diff --git a/stylecop.analyzers.ruleset b/stylecop.analyzers.ruleset
index 3c61a4c..660192c 100644
--- a/stylecop.analyzers.ruleset
+++ b/stylecop.analyzers.ruleset
@@ -9,6 +9,8 @@
         <Rule Id="CA1009" Action="Warning"/>
         <Rule Id="CA1016" Action="Warning"/>
         <Rule Id="CA1033" Action="Warning"/>
+        <Rule Id="CA1034" Action="None"/>
+        <Rule Id="CA1033" Action="Warning"/>
         <Rule Id="CA1049" Action="Warning"/>
         <Rule Id="CA1060" Action="Warning"/>
         <Rule Id="CA1061" Action="Warning"/>
diff --git a/tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs b/tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs
index 655a296..44d8528 100644
--- a/tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs
+++ b/tests/LinkDotNet.StringBuilder.UnitTests/ValueStringBuilderTests.cs
@@ -489,4 +489,18 @@ public void GivenAString_WhenCallingToStringWithRange_ThenShouldReturnSubstring(
 
         builder.ToString(1..4).Should().Be("ell");
     }
+
+    [Fact]
+    public void GivenAString_WhenEnumerating_ThenShouldReturnCharacters()
+    {
+        using var builder = new ValueStringBuilder("Hello World");
+        var output = string.Empty;
+
+        foreach (var c in builder)
+        {
+            output += c;
+        }
+
+        output.Should().Be("Hello World");
+    }
 }
\ No newline at end of file