add Encoding GetChars

Author: SimonCropp

apiCount.include.md

@@ -1 +1 @@
-**API count: 455**
+**API count: 456**

api_list.include.md

@@ -90,6 +90,7 @@
  * `int GetByteCount(Encoding, ReadOnlySpan<char>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getbytecount#system-text-encoding-getbytecount(system-readonlyspan((system-char))))
  * `int GetBytes(Encoding, ReadOnlySpan<char>, Span<byte>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getbytes#system-text-encoding-getbytes(system-readonlyspan((system-char))-system-span((system-byte))))
  * `int GetCharCount(Encoding, ReadOnlySpan<byte>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getcharcount#system-text-encoding-getcharcount(system-readonlyspan((system-byte))))
+ * `int GetChars(Encoding, ReadOnlySpan<byte>, Span<char>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getchars#system-text-encoding-getchars(system-readonlyspan((system-byte))-system-span((system-char))))
  * `string GetString(Encoding, ReadOnlySpan<byte>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getstring#system-text-encoding-getstring(system-readonlyspan((system-byte))))
 
 

readme.md

@@ -12,7 +12,7 @@ The package targets `netstandard2.0` and is designed to support the following ru
  * `net5.0`, `net6.0`, `net7.0`, `net8.0`, `net9.0`
 
 
-**API count: 455**<!-- singleLineInclude: apiCount. path: /apiCount.include.md -->
+**API count: 456**<!-- singleLineInclude: apiCount. path: /apiCount.include.md -->
 
 
 **See [Milestones](../../milestones?state=closed) for release notes.**
@@ -559,6 +559,7 @@ The class `Polyfill` includes the following extension methods:
  * `int GetByteCount(Encoding, ReadOnlySpan<char>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getbytecount#system-text-encoding-getbytecount(system-readonlyspan((system-char))))
  * `int GetBytes(Encoding, ReadOnlySpan<char>, Span<byte>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getbytes#system-text-encoding-getbytes(system-readonlyspan((system-char))-system-span((system-byte))))
  * `int GetCharCount(Encoding, ReadOnlySpan<byte>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getcharcount#system-text-encoding-getcharcount(system-readonlyspan((system-byte))))
+ * `int GetChars(Encoding, ReadOnlySpan<byte>, Span<char>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getchars#system-text-encoding-getchars(system-readonlyspan((system-byte))-system-span((system-char))))
  * `string GetString(Encoding, ReadOnlySpan<byte>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getstring#system-text-encoding-getstring(system-readonlyspan((system-byte))))
 
 

src/Polyfill/Polyfill_Encoding_GetChars.cs

@@ -0,0 +1,39 @@
+// <auto-generated />
+
+#pragma warning disable
+
+#if FeatureMemory
+
+namespace Polyfills;
+
+using System;
+using System.Runtime.InteropServices;
+using System.Text;
+
+static partial class Polyfill
+{
+#if NETCOREAPP2_0 || NETFRAMEWORK || NETSTANDARD2_0
+    /// <summary>
+    /// Decodes all the bytes in the specified read-only byte span into a character span.
+    /// </summary>
+    /// <param name="chars">The character span receiving the decoded bytes.</param>
+    /// <returns>The actual number of characters written at the span indicated by the chars parameter.</returns>
+    //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.encoding.getchars#system-text-encoding-getchars(system-readonlyspan((system-byte))-system-span((system-char)))
+    public static int GetChars(this Encoding target, ReadOnlySpan<byte> bytes, Span<char> chars)
+    {
+        if (target is null)
+        {
+            throw new ArgumentNullException(nameof(target));
+        }
+
+        char[] charArray = new char[bytes.Length];
+        var array = bytes.ToArray();
+        var count = target.GetChars(array, 0, bytes.Length, charArray, 0);
+        new ReadOnlySpan<char>(charArray).CopyTo(chars);
+        return count;
+    }
+#endif
+
+}
+
+#endif

src/Tests/PolyfillTests_Encoding.cs

@@ -11,6 +11,24 @@ public void Encoding_GetByteCount()
         Assert.AreEqual(13, byteCount);
     }
 
+    [Test]
+    public void Encoding_GetChars()
+    {
+        // Arrange
+        var encoding = Encoding.UTF8;
+        var utf8Bytes = "Hello, World!"u8.ToArray();
+        var byteSpan = new ReadOnlySpan<byte>(utf8Bytes);
+        var charArray = new char[utf8Bytes.Length];
+        var charSpan = new Span<char>(charArray);
+
+        // Act
+        var charCount = encoding.GetChars(byteSpan, charSpan);
+
+        // Assert
+        var result = charSpan.Slice(0, charCount).ToString();
+        Assert.AreEqual("Hello, World!", result);
+    }
+
     [Test]
     public void Encoding_GetString()
     {