std::conditional (3) - Linux Manuals

std::conditional: std::conditional

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.

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