std::conditional - cppreference.com
From cppreference.com
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(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.
Member types
| Member type | Definition |
type
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T if B == true, F if B == false
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Helper types
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(since C++14) | |
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; };
Example
#include <iostream> #include <type_traits> #include <typeinfo> 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:
See also
| conditionally removes a function overload or template specialization from overload resolution (class template) [edit] |