Defined in header <type_traits> template< bool B, class T, class F >
struct conditional; (since C++11)
Provides member typedef type, which is defined as T if B is true at compile time, or as F if B is false.
Member types
Member type Definition type T if B == true, F if B == false
Helper types
template< bool B, class T, class F >
using conditional_t = typename conditional<B,T,F>::type; (since C++14)
Possible implementation
templa