Namespace Association
7.9 Namespace Association
Caution: The semantics of this extension are equivalent to C++ 2011 inline namespaces. Users should use inline namespaces instead as this extension will be removed in future versions of G++.
A using-directive with __attribute ((strong)) is stronger than a normal using-directive in two ways:
- Templates from the used namespace can be specialized and explicitly instantiated as though they were members of the using namespace.
- The using namespace is considered an associated namespace of all templates in the used namespace for purposes of argument-dependent name lookup.
The used namespace must be nested within the using namespace so that normal unqualified lookup works properly.
This is useful for composing a namespace transparently from implementation namespaces. For example:
namespace std {
name