Creating an alias for a nested namespace (C++ only)

Namespace definitions hold declarations. Since a namespace definition is a declaration itself, namespace definitions can be nested.

namespace INTERNATIONAL_BUSINESS_MACHINES {
  int j;
  namespace NESTED_IBM_PRODUCT {
    void a() { j++; }
    int j;
    void b() { j++; }
  }
}
namespace NIBM = INTERNATIONAL_BUSINESS_MACHINES::NESTED_IBM_PRODUCT;

In this example, the NIBM identifier is an alias for the namespace NESTED_IBM_PRODUCT. This namespace is nested within the INTERNATIONAL_BUSINESS_MACHINES namespace.