Question

I just upgraded a VS 2005 project to VS 2008 and was examining the changes. I noticed one of the .Designer.cs files had changed significantly. The majority of the changes were simply replacements of System with global::System. For example,

protected override System.Data.DataTable CreateInstance() 

became

protected override global::System.Data.DataTable CreateInstance() 

What’s going on here?

Answer 1

The :: operator is called a Namespace Alias Qualifier.

 global::System.Data.DataTable  

is the same as:

 System.Data.DataTable 

Visual Studio 2008 added it to the designer generated code to avoid ambigious reference issues that occasionally happened when people created classes named System…For example:

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);     } } 

However:

global::System.Console.Writeline('This works'); 

For further reading:

http://msdn.microsoft.com/en-us/library/c3ay4x3d(VS.80).aspx