Is there any performance increase by changing this .NET string to a const? Does the IL automatically do that?

Question

Given the following simple .NET code, is there any difference between these two, under the hood with respect to the string \"xml\"?

if (extension.Eq         


        

Answer 1

There is no difference due to the fact that literal strings are normally interned by the compiler.

All the following examples will print out true:

• Example 1:

  const string constHello = "Hello";
  
  void Foo()
  {
      var localHello = "Hello";
      Console.WriteLine(ReferenceEquals(constHello, localHello));
  }
  

• Example 2:

  string fieldHello = "Hello";        
  
  void Foo()
  {
      var localHello= "Hello";
      Console.WriteLine(ReferenceEquals(fieldHello, localHello));
  }
  

• Example 3:

  const string constHello = "Hello";
  
  void Foo()
  {
      Console.WriteLine({IsReferenceEquals("Hello")}");
  }
  
  public static bool IsReferenceEquals(string s) => ReferenceEquals(constHello, s);
  

In all cases, there is only one instance of "Hello".