std::conditional
From cppreference.com
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.
Contents |
[edit] Member types
Member type | Definition |
type
|
T if B == true, F if B == false
|
[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 { typedef T type; }; template<class T, class F> struct conditional<false, T, F> { typedef F type; }; |
[edit] Example
Run this code
#include <iostream> #include <type_traits> #include <typeinfo> int main() { typedef std::conditional<true, int, double>::type Type1; typedef std::conditional<false, int, double>::type Type2; typedef std::conditional<sizeof(int) >= sizeof(double), int, double>::type Type3; std::cout << typeid(Type1).name() << '\n'; std::cout << typeid(Type2).name() << '\n'; std::cout << typeid(Type3).name() << '\n'; }
Output:
i d d
[edit] See also
(C++11)
|
hides a function overload or template specialization based on compile-time boolean (class template) |