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std::conditional

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Definido no cabeçalho <type_traits>
template< bool B, class T, class F >
struct conditional;
 (desde C++11)
Fornece type membro typedef, que é definido como T se B é true em tempo de compilação, ou como se F B é false.
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Provides member typedef type, which is defined as T if B is true at compile time, or as F if B is false.
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Índice

[editar] Tipos de membro

Tipo de membro
Original:
Member type
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 Definition
type T if B == true, F if B == false

[editar] Possível implementação

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; };

[editar] Exemplo

#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';
}

Saída: 

i
d
d

[editar] Veja também

(C++11)
esconde uma sobrecarga de função ou especialização de modelo com base em tempo de compilação boolean
Original:
hides a function overload or template specialization based on compile-time boolean
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(modelo de classe) [edit]
Obtida de "https://pt.cppreference.com/mwiki/index.php?title=cpp/types/conditional&oldid=24538"