std::conditional - cppreference.com (original) (raw)

| | | | | --------------------------------------------------------- | | ------------- | | 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.

If the program adds specializations for std::conditional, the behavior is undefined.

[edit] Member types

[edit] Helper types

| template< bool B, class T, class F > using conditional_t = typename conditional<B,T,F>::type; | | (since C++14) | | ------------------------------------------------------------------------------------------------- | | ------------- |

[edit] Possible implementation

template<bool B, class T, class F> struct conditional { using type = T; };   template<class T, class F> struct conditional<false, T, F> { using type = F; };

[edit] Example

#include #include #include   int main() { using Type1 = std::conditional<true, int, double>::type; using Type2 = std::conditional<false, int, double>::type; using Type3 = std::conditional<sizeof(int) >= sizeof(double), int, double>::type;   std::cout << typeid(Type1).name() << '\n'; std::cout << typeid(Type2).name() << '\n'; std::cout << typeid(Type3).name() << '\n'; }

Possible output:

[edit] See also

| | conditionally removes a function overload or template specialization from overload resolution (class template) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |