cmake/Tests/CompileFeatures/cxx_inline_namespaces.cpp

namespace Lib
{
inline namespace Lib_1
{
  template <typename T> class A;
}

template <typename T> void g(T);
}

struct MyClass {

};
namespace Lib
{
template<>
class A<MyClass> {

};
}

void someFunc()
{
  Lib::A<MyClass> a;
  g(a);  // ok, Lib is an associated namespace of A
}