Std::conditional (3) Linux Manual Page

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.

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 { 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

std::conditional (3) Linux Manual Page