What is the usage of global:: keyword in C#?

Question

What is the usage of global:: keyword in C#? When must we use this keyword?

Answer 1

Technically, global is not a keyword: it's a so-called "contextual keyword". These have special meaning only in a limited program context and can be used as identifiers outside that context.

global can and should be used whenever there's ambiguity or whenever a member is hidden. From here:

class TestApp {     // Define a new class called 'System' to cause problems.     public class System { }      // Define a constant called 'Console' to cause more problems.     const int Console = 7;     const int number = 66;      static void Main()     {         // Error  Accesses TestApp.Console         Console.WriteLine(number);         // Error either         System.Console.WriteLine(number);         // This, however, is fine         global::System.Console.WriteLine(number);     } } 

Note, however, that global doesn't work when no namespace is specified for the type:

// See: no namespace here public static class System {     public static void Main()     {         // "System" doesn't have a namespace, so this         // will refer to this class!         global::System.Console.WriteLine("Hello, world!");     } }