C++ templates: how to determine if a type is suitable for subclassing -


let's have templated class depending on type t. t anything: int, int*, pair <int, int> or struct lol; cannot void, reference or cv-qualified though. optimization need know if can subclass t. so, i'd need trait type is_subclassable, determined logical combination of basic traits or through sfinae tricks.

in original example, int , int* not subclassable, while pair <int, int> , struct lol are.

edit: litb pointed out below, unions not subclassable , t can union type well.

how write trait type need?

you want determine whether non-union class. there no way known me (and boost hasn't found way either). if can live union cases false positives, can use is_class.

template<typename> struct void_ { typedef void type; };  template<typename t, typename = void> struct is_class { static bool const value = false; };  template<typename t> struct is_class<t, typename void_<int t::*>::type> {    static bool const value = true;  };

boost has is_union uses compiler-specific builtins though, here. is_class (which boost provides) combined is_union solve problem.


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