| 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.
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
#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
See also
| (C++11) | hides a function overload or template specialization based on compile-time boolean (class template) |
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