C# 4.0 Pocket Reference, 3rd Edition

Namespaces

A namespace is a domain within which type names must be unique. Types are typically organized into hierarchical namespaces—both to avoid naming conflicts and to make type names easier to find. For example, the RSA type that handles public key encryption is defined within the following namespace:

System.Security.Cryptography

A namespace forms an integral part of a type’s name. The following code calls RSA’s Create method:

System.Security.Cryptography.RSA rsa =
  System.Security.Cryptography.RSA.Create();

Note

Namespaces are independent of assemblies, which are units of deployment such as an .exe or .dll.

Namespaces also have no impact on member accessibility: public, internal, private, and so on.

The namepace keyword defines a namespace for types within that block. For example:

namespace Outer.Middle.Inner
{
  class Class1 {}
  class Class2 {}
}

The dots in the namespace indicate a hierarchy of nested namespaces. The code that follows is semantically identical to the preceding example.

namespace Outer
{
  namespace Middle
  {
    namespace Inner
    {
      class Class1 {}
      class Class2 {}
    }
  }
}

You can refer to a type with its fully qualified name, which includes all namespaces from the outermost to the innermost. For example, we could refer to Class1 in the preceding example as Outer.Middle.Inner.Class1.

Types not defined in any namespace are said to reside in the global namespace. The global namespace also includes top-level namespaces, such as Outer in our example.

The using Directive

The using directive ...