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.
The behavior of a program that adds specializations for conditional is undefined.
| Member type | Definition |
|---|---|
type | T if B == true, F if B == false |
template< bool B, class T, class F > using conditional_t = typename conditional<B,T,F>::type; | (since C++14) |
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; }; |
#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:
int double double
|
(C++11) | conditionally removes a function overload or template specialization from overload resolution (class template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/types/conditional