Alias quantifier Operator

The 'namespace alias qualifier' (::) is used in C# for resolving namespace conflicts.

It's mainly used in combination with the 'global' keyword - which denotes the root or global namespace - though it can also be used with 'extern' aliases.

Here's an example:

using System;

namespace N

{

   class A

   {

      static void Main()

      {

         Console.WriteLine(new A.B());

         Console.WriteLine(new global::A.B());

         Console.ReadKey();

      }

      public class B {} 

   }

namespace A

{

   class B {}

}

If you run this, the output is:

N.A+B

A.B

So, with the first line, the compiler thinks you mean the nested class B, within class A, within namespace N.

If we want to access class B within namespace A, then we need to qualify A.B() with global:: to make it clear that we're starting from the global namespace.