NAME

std::conditional - std::conditional

Synopsis

Defined in header <type_traits>
template< bool B, class T, class F > (since C++11)
struct conditional;

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 types

Member type Definition
type T if B == true, F if B == false

Helper types

template< bool B, class T, class F > (since C++14)
using conditional_t = typename conditional<B,T,F>::type;

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

// 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