c++ - Private Class within Namespace -

i have class within namespace in header file. class requires template type, , want types used. below shows example.

file a.hpp

// a.hpp namespace a_ns { template<class t>     class {     // stuff }; typedef a<double> a_double; } // end of namespace // stuff 

file b.hpp

// b.hpp #include <a.hpp> namespace b_ns {     typedef a_ns::a_double b; } 

file main.cpp

// main.cpp #include "b.hpp" int main() {     b_ns::b my_b; // <<<--- this!     a_ns::a<float> my_a_which_is_not_allowed; // <<<--- not though! d: } 

so can see rather longed out example, end objective not allow end user declare class a float typename, , able use pre-defined classes specific types, declared typedef a<double> a_double;.

i thought example above allow this, wrong, can create a<float> above, because include b.hpp, in turn includes a.hpp! see problem! (hopefully?)

there simple solution, if @ possible.

if want able use type aliases , not use a directly, can put implementation namespace users should know not use:

namespace a_ns {  namespace detail {     template<class t>             class {         // stuff     }; }  typedef detail::a<double> a_double; } // end of namespace 

now can use a_double, use a directly, detail namespace have dug into, , that's accepted bad thing do. if user decides want that, they've given on staying out of trouble , shouldn't take measures stop them hurting themself.