c++ Templates to change constness of a function -

i interested in designing template interface const ness of function , return type changes depending on template parameter. have managed return type follows.

template<typename t, bool canchange> struct changable{};  template<typename t> struct changable<t,true> {     typedef t type; };  template<typename t> struct changable<t,false> {     typedef const t type; };  template<typename t, bool canchange> struct data{     typedef typename changable<t,canchange>::type datatype;             datatype m_data; //< makes const/non-const @ compile time.      // function make return type const/non-const      // @ compile time.      datatype& getdataref(){ return m_data;}       //however, seems me still need second function      //with explicit "const", can't seem avoid.     datatype& getdataref()const{return m_data;} }; 

can somehow avoid having 2 const/non-const functions here @ compile time using sfinae magic? std::enable_if have been ideal here seems me const not type , approach may not work. suggestions?

here example based on inheritance:

#include <type_traits> #include <iostream>  template<typename t, bool canchange> struct changable { using type = const t; };  template<typename t>  struct changable<t, true> { using type = std::decay_t<t>; };  template<typename, typename, bool> struct base;  template<typename d, typename t> struct base<d, t, true> {     using datatype = typename changable<t, true>::type;     datatype& getdataref() { std::cout << "non-const" << std::endl; return static_cast<d*>(this)->m_data; } };  template<typename d, typename t> struct base<d, t, false> {     using datatype = typename changable<t, false>::type;     datatype& getdataref() const { std::cout << "const" << std::endl; return static_cast<const d*>(this)->m_data; } };  template<typename t, bool canchange> struct data: base<data<t, canchange>, t, canchange> {     friend class base<data<t, canchange>, t, canchange>;     typename base<data<t, canchange>, t, canchange>::datatype m_data{};     using base<data<t, canchange>, t, canchange>::getdataref; };  int main() {     data<int, true> d1;     data<int, false> d2;     d1.getdataref();     d2.getdataref(); } 

as requested, data has 1 definition of getdataref method.
1 available, const 1 or other one, depends on value of canchange.

note friend declaration. allows base class access private data members of data.