c++ - How to specialize templated class methods based on type traits? Using std::enable_if works for non-class functions, but fails for class methods -

i've been trying create specializations of templated class methods such have different method definitions compiler selects based on whether argument integral type of enum class, clang gives me error:

out-of-line definition of 'parsestring' not match declaration in 'mydata'

while gcc gives following:

error: prototype 'typename std::enable_if::value, void>::type mydata::parsestring(t&, std::string)' not match in class 'mydata'

error: candidate is: template static void mydata::parsestring(t&, std::string)

the following code used produce these errors. i've experimented other ways of using enable_if, such in template parameter rather return type, nothing far has worked. if make templated functions non-class functions instead of class methods, work fine. (removing static makes no difference.)

is there way use enable_if templated class methods, or better way achieve same thing?

#include <string> #include <type_traits> #include <utility>  class mydata { public:     mydata() = default;     mydata(std::pair<std::string, std::string> string_representations);     std::pair<std::string, std::string> tostrings();      enum class myenum     {         = 0,         b = 1     };      int integral_value;     myenum enum_value;  private:      template<typename t>     static void parsestring(t&, std::string); };  mydata::mydata(std::pair<std::string, std::string> string_representations) {     parsestring(integral_value, string_representations.first);     parsestring(enum_value, string_representations.second); }  std::pair<std::string, std::string> mydata::tostrings() {     return std::make_pair(std::to_string(integral_value), std::to_string((unsigned long)enum_value)); }  template<typename t> typename std::enable_if<std::is_enum<t>::value, void>::type     mydata::parsestring(t& setting, std::string representation) {     setting = (t)std::stoul(representation); }  template<typename t> typename std::enable_if<std::is_integral<t>::value, void>::type     mydata::parsestring(t& setting, std::string representation) {     setting = std::stoi(representation); } 

(in example there's 1 integral , 1 enum member of class, if you're wondering why templated function useful, imagine if class had multiple different enum , integral type members.)

the error telling signature in definition of parsestring method doesn't match found in declaration inside class. have copy enable_if , use in declaration well.

template<typename t> static typename std::enable_if<std::is_integral<t>::value, void>::type parsestring(t&, std::string); 

you need declaration of parsestring uses enable_if<is_enum<t>> in declaration, since define function uses it:

template<typename t> static typename std::enable_if<std::is_enum<t>::value, void>::type parsestring(t&, std::string);