src/.editorconfig

@@ -335,6 +335,8 @@ resharper_return_value_of_pure_method_is_not_used_highlighting = error
 
 resharper_all_underscore_local_parameter_name_highlighting = none
 
+resharper_misleading_body_like_statement_highlighting = error
+
 # Xml files
 [*.{xml,config,nuspec,resx,vsixmanifest,csproj,targets,props,fsproj}]
 indent_size = 2

src/Directory.Build.props

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
   <PropertyGroup>
-    <Version>7.21.0</Version>
+    <Version>7.22.0</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>Polyfill</PackageTags>
     <DisableImplicitNamespaceImports>true</DisableImplicitNamespaceImports>

src/Directory.Packages.props

@@ -9,7 +9,7 @@
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.13.0" />
     <PackageVersion Include="NUnit" Version="3.14.0" />
     <PackageVersion Include="NUnit3TestAdapter" Version="5.0.0" />
-    <PackageVersion Include="ProjectDefaults" Version="1.0.148" />
+    <PackageVersion Include="ProjectDefaults" Version="1.0.149" />
     <PackageVersion Include="System.Memory" Version="4.6.0" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
     <PackageVersion Include="Microsoft.Bcl.Memory" Version="9.0.1" />

src/Polyfill/Polyfill_StringBuilder_AppendJoin.cs

@@ -1,10 +1,13 @@
 // <auto-generated />
 #pragma warning disable
 
+#nullable enable
+
 namespace Polyfills;
 
 using System;
 using System.Text;
+using System.Collections.Generic;
 
 static partial class Polyfill
 {
@@ -17,63 +20,196 @@ public static StringBuilder AppendJoin<T>(
         this StringBuilder target,
         char separator,
         IEnumerable<T> values) =>
-        target.Append(string.Join(separator.ToString(), values));
+        target.AppendJoinCore(separator, values);
 
     /// <summary>Concatenates and appends the members of a collection, using the specified char separator between each member.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin-1(system-char-system-collections-generic-ienumerable((-0)))
     public static StringBuilder AppendJoin<T>(
         this StringBuilder target,
-        string separator,
+        string? separator,
         IEnumerable<T> values) =>
-        target.Append(string.Join(separator, values));
+        target.AppendJoinCore(separator ?? string.Empty, values);
 
     /// <summary>Concatenates the strings of the provided array, using the specified separator between each string, then appends the result to the current instance of the string builder.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin(system-string-system-string())
     public static StringBuilder AppendJoin(
         this StringBuilder target,
-        string separator,
-        params string[] values) =>
-        target.Append(string.Join(separator, values));
+        string? separator,
+        params string?[] values) =>
+        target.AppendJoinCore(separator ?? string.Empty, values);
 
     /// <summary>Concatenates the string representations of the elements in the provided array of objects, using the specified separator between each member, then appends the result to the current instance of the string builder.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin(system-string-system-object())
     public static StringBuilder AppendJoin(
         this StringBuilder target,
-        string separator,
-        params Object[] values) =>
-        target.Append(string.Join(separator, values));
+        string? separator,
+        params object?[] values) =>
+        target.AppendJoinCore(separator ?? string.Empty, values);
 
     /// <summary>Concatenates the strings of the provided array, using the specified char separator between each string, then appends the result to the current instance of the string builder.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin(system-char-system-string())
     public static StringBuilder AppendJoin(
         this StringBuilder target,
         char separator,
-        params string[] values) =>
-        target.Append(string.Join(separator.ToString(), values));
+        params string?[] values) =>
+        target.AppendJoinCore(separator, values);
 
     /// <summary>Concatenates the string representations of the elements in the provided array of objects, using the specified char separator between each member, then appends the result to the current instance of the string builder.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin(system-char-system-object())
     public static StringBuilder AppendJoin(
         this StringBuilder target,
         char separator,
-        params object[] values) =>
-        target.Append(string.Join(separator.ToString(), values));
+        params object?[] values) =>
+        target.AppendJoinCore(separator, values);
 
     /// <summary>Concatenates and appends the members of a collection, using the specified char separator between each member.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin-1(system-char-system-collections-generic-ienumerable((-0)))
     public static StringBuilder AppendJoin<T>(
         this StringBuilder target,
         char separator,
         params T[] values) =>
-        target.Append(string.Join(separator.ToString(), values));
+        target.AppendJoinCore(separator, values);
 
     /// <summary>Concatenates and appends the members of a collection, using the specified char separator between each member.</summary>
     //Link: https://learn.microsoft.com/en-us/dotnet/api/system.text.stringbuilder.appendjoin#system-text-stringbuilder-appendjoin-1(system-string-system-collections-generic-ienumerable((-0)))
     public static StringBuilder AppendJoin<T>(
         this StringBuilder target,
         string separator,
         params T[] values) =>
-        target.Append(string.Join(separator.ToString(), values));
+        target.AppendJoinCore(separator, values);
+
+    private static StringBuilder AppendJoinCore<T>(
+        this StringBuilder target,
+        char separator,
+        IEnumerable<T> values)
+    {
+        if (values == null)
+        {
+            throw new ArgumentNullException(nameof(values));
+        }
+
+        using (IEnumerator<T> en = values.GetEnumerator())
+        {
+            if (!en.MoveNext())
+            {
+                return target;
+            }
+
+            T value = en.Current;
+            if (value != null)
+            {
+                target.Append(value.ToString());
+            }
+
+            while (en.MoveNext())
+            {
+                target.Append(separator);
+                value = en.Current;
+                if (value != null)
+                {
+                    target.Append(value.ToString());
+                }
+            }
+        }
+        return target;
+    }
+
+    private static StringBuilder AppendJoinCore<T>(
+        this StringBuilder target,
+        char separator,
+        T[] values)
+    {
+        if (values == null)
+        {
+            throw new ArgumentNullException(nameof(values));
+        }
+
+        if (values.Length == 0)
+        {
+            return target;
+        }
+
+        if (values[0] != null)
+        {
+            target.Append(values[0]!.ToString());
+        }
+
+        for (int i = 1; i < values.Length; i++)
+        {
+            target.Append(separator);
+            if (values[i] != null)
+            {
+                target.Append(values[i]!.ToString());
+            }
+        }
+        return target;
+    }
+
+    private static StringBuilder AppendJoinCore<T>(
+        this StringBuilder target,
+        string separator,
+        IEnumerable<T> values)
+    {
+        if (values == null)
+        {
+            throw new ArgumentNullException(nameof(values));
+        }
+
+        using (IEnumerator<T> en = values.GetEnumerator())
+        {
+            if (!en.MoveNext())
+            {
+                return target;
+            }
+
+            T value = en.Current;
+            if (value != null)
+            {
+                target.Append(value.ToString());
+            }
+
+            while (en.MoveNext())
+            {
+                target.Append(separator);
+                value = en.Current;
+                if (value != null)
+                {
+                    target.Append(value.ToString());
+                }
+            }
+        }
+        return target;
+    }
+
+    private static StringBuilder AppendJoinCore<T>(
+        this StringBuilder target,
+        string separator,
+        T[] values)
+    {
+        if (values == null)
+        {
+            throw new ArgumentNullException(nameof(values));
+        }
+
+        if (values.Length == 0)
+        {
+            return target;
+        }
+
+        if (values[0] != null)
+        {
+            target.Append(values[0]!.ToString());
+        }
 
+        for (int i = 1; i < values.Length; i++)
+        {
+            target.Append(separator);
+            if (values[i] != null)
+            {
+                target.Append(values[i]!.ToString());
+            }
+        }
+        return target;
+    }
 #endif
 }

src/global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "10.0.100-preview.3.25125.17",
+    "version": "10.0.100-preview.3.25156.15",
     "allowPrerelease": true,
     "rollForward": "latestFeature"
   }