From 76048c739addb3da99ce12e886ded090753b5579 Mon Sep 17 00:00:00 2001
From: James Ko <jamesqko@gmail.com>
Date: Thu, 25 Aug 2016 18:01:02 -0400
Subject: [PATCH] Avoid unnecessary indirection in char.ToString (#6903)

Avoid unnecessary indirection in char.ToString
---
 src/mscorlib/src/System/Char.cs   |  5 +----
 src/mscorlib/src/System/String.cs | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/mscorlib/src/System/Char.cs b/src/mscorlib/src/System/Char.cs
index c7fd4b3..ff936c6 100644
--- a/src/mscorlib/src/System/Char.cs
+++ b/src/mscorlib/src/System/Char.cs
@@ -163,10 +163,7 @@ namespace System {
       ==============================================================================*/
       // Provides a string representation of a character.
       [Pure]
-      public static String ToString(char c) {
-          Contract.Ensures(Contract.Result<String>() != null);
-          return new String(c, 1);
-      }
+      public static string ToString(char c) => string.CreateFromChar(c);
 
       public static char Parse(String s) {
           if (s==null) {
diff --git a/src/mscorlib/src/System/String.cs b/src/mscorlib/src/System/String.cs
index 841af22..2956c42 100644
--- a/src/mscorlib/src/System/String.cs
+++ b/src/mscorlib/src/System/String.cs
@@ -25,6 +25,7 @@ namespace System {
     using System.Runtime.Versioning;
     using Microsoft.Win32;
     using System.Diagnostics.Contracts;
+    using System.Security;
 
     //
     // For Information on these methods, please see COMString.cpp
@@ -1488,7 +1489,6 @@ namespace System {
             return TrimHelper(trimChars,TrimTail);
         }
     
-    
         // Creates a new string with the characters copied in from ptr. If
         // ptr is null, a 0-length string (like String.Empty) is returned.
         //
@@ -1567,6 +1567,17 @@ namespace System {
 
             return s;
         }
+
+        // This is only intended to be used by char.ToString.
+        // It is necessary to put the code in this class instead of Char, since m_firstChar is a private member.
+        // Making m_firstChar internal would be dangerous since it would make it much easier to break String's immutability.
+        [SecuritySafeCritical]
+        internal static string CreateFromChar(char c)
+        {
+            string result = FastAllocateString(1);
+            result.m_firstChar = c;
+            return result;
+        }
                 
         [System.Security.SecuritySafeCritical]  // auto-generated
         unsafe internal int GetBytesFromEncoding(byte* pbNativeBuffer, int cbNativeBuffer,Encoding encoding)
-- 
2.7.4