c++ - Achieving an SFINAE-like effect in an if-else block -

i able write like

template <typename t> void foo() {     // ...     if (is_nice<t>::value) {         bar_which_is_defined_only_for_nice_types<t>();     } } 

however, when try compile (g++ 4.9.3, no optimization) complaint bar_which_is_defined_only_for_nice_types. how can achieve desired effect without resorting 2 definitions of foo()?

you can tag dispatch based on is_nice<t>

#include <type_traits>  template<typename t> struct is_nice : std::false_type {}; template<> struct is_nice<int> : std::true_type {};  template<typename t> void do_nice_things(std::true_type) {     bar_which_is_defined_only_for_nice_types<t>(); }  template<typename t> void do_nice_things(std::false_type) { }  template <typename t> void foo() {     do_nice_things<t>(is_nice<t>{}); }