c++ - Only overload operator if template argument does -

given template class single template argument t, possible overload operators in available type t? example:

template <typename t> class { public:     #if hasoperator(t, +=)     t& operator +=(const t &rhs)     {         mvalue += rhs;         return mvalue;     }     #endif  private:     t mvalue; }   int main() {     a<int> a;     += 8; //+= forward += int      struct test {  /*no operators defined*/ };     a<test> b; //+= not implemented since test not implement += } 

i'm writting generic wrapper class needs behave template type. if t has operator +=, (at compile time) overload += accordingly. yes, go ahead , implement every operator in a, compiler error when t doesn't have operator. @ first though template specialization might answer, require specialization every type. while work , lot of typing, wont because needs work type (not specialized).

use expression sfinae drop operator+ overload resolution set unless t defines operator+

template <typename t> class { private:     t mvalue; public:     template<typename u=t>     auto operator +=(const u &rhs)         -> decltype(mvalue += rhs)     {         mvalue += rhs;         return mvalue;     } }; 

live demo