Difference between revisions of "cpp/types/conditional"
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Revision as of 11:44, 16 September 2020
| 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.
If the program adds specializations for std::conditional, the behavior is undefined.
Contents |
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
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; }; |
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'; }
Possible output:
int double double
See also
| (C++11) |
conditionally removes a function overload or template specialization from overload resolution (class template) |
