C# Language Specification

Fully qualified names

Every namespace and type has a fully qualified name, which uniquely identifies the namespace or type amongst all others. The fully qualified name of a namespace or type N is determined as follows:

• 
  If N is a member of the global namespace, its fully qualified name is N.
  
• 
  Otherwise, its fully qualified name is S.N, where S is the fully qualified name of the namespace or type in which N is declared.
  

In other words, the fully qualified name of N is the complete hierarchical path of identifiers that lead to N, starting from the global namespace. Because every member of a namespace or type must have a unique name, it follows that the fully qualified name of a namespace or type is always unique.

The example below shows several namespace and type declarations along with their associated fully qualified names.

class A {} // A

namespace X // X

{
class B // X.B
{
class C {} // X.B.C
}

namespace Y // X.Y

{
class D {} // X.Y.D
}
}

namespace X.Y // X.Y

{
class E {} // X.Y.E
}

9.