Why are some functions in not in the std namespace?

Question

I am developing a project which works with multiple arithmetic types. So I made a header, where the minimal requirements for a user defined arithmetic type are defined:

Answer 1

This is just a humble attempt to start solving this problem. (Suggestions are welcomed.)

I have been dealing with this problem a long time. A case were the problem is very obvious is this case:

#include
#include

namespace mylib{
    std::string exp(double x){return "mylib::exp";}
}

int main(){
    std::cout << std::exp(1.) << std::endl; // works
    std::cout << mylib::exp(1.) << std::endl; // works

    using namespace mylib;
    std::cout << exp(1.) << std::endl; //doesn't works!, "ambiguous" call
    return 0;
}

This is in my opinion is an annoying bug or at the least an very unfortunate situation. (At least in GCC, and clang --using GCC library-- in Linux.)

Lately I gave it another shot to the problem. By looking at the cmath (of GCC) it seems that the header is there simply to overload the C-functions and screws up the namespace in the process.

namespace std{
   #include
}
//instead of #include

With it this works

using namespace mylib;
std::cout << exp(1.) << std::endl; //now works.

I am almost sure that this is not exactly equivalent to #include but most functions seem to work.

Worst of all is that eventually some dependence library will eventually will #inclulde. For that I couldn't find a solution yet.

NOTE: Needless to say this doesn't work at all

namespace std{
   #include // compile errors
}