std::forward

 

C++

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Utilidades de la biblioteca

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Objetos Function

initializer_list (C++11)

bitset

hash (C++11)

Operadores relacionales Original: Relational operators The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

Pares y tuplas Original: Pairs and tuples The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

Cambiar, hacia adelante y mover Original: Swap, forward and move The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

swap

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

declval (C++11)

 

Definido en la cabecera <utility>
template< class T > T&& forward( typename std::remove_reference<T>::type& t );	(1)	(desde C++11)
template< class T > T&& forward( typename std::remove_reference<T>::type&& t );	(2)	(desde C++11)

Cuando se usa de acuerdo con la siguiente receta en una plantilla de función, reenvía el argumento a otra función exactamente como se lo pasa a la función de llamada .

Original:

When used according to the following recipe in a function template, forwards the argument to another function exactly as it was passed to the calling function.

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template<typename T>
wrapper(T&& arg) {
  foo(std::forward<T>(arg));
}

• Si una llamada a wrapper() pasa un std::string valor p, entonces se deduce a T std::string (no std::string&, const std::string&, o std::string&&), y std::forward asegura que un valor p de referencia se pasa a foo .

  Original:

  If a call to wrapper() passes an rvalue std::string, then T is deduced to std::string (not std::string&, const std::string&, or std::string&&), and std::forward ensures that an rvalue reference is passed to foo.

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• Si una llamada a wrapper() pasa un const std::string lvalue, entonces se deduce a T const std::string&, y std::forward asegura que una referencia const lvalue se pasa a foo .

  Original:

  If a call to wrapper() passes a const lvalue std::string, then T is deduced to const std::string&, and std::forward ensures that a const lvalue reference is passed to foo.

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• Si una llamada a wrapper() pasa un std::string no constante lvalue, entonces se deduce que T std::string& y std::forward asegura que una referencia no const lvalue se pasa a foo .

  Original:

  If a call to wrapper() passes a non-const lvalue std::string, then T is deduced to std::string&, and std::forward ensures that a non-const lvalue reference is passed to foo.

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Notas

Al intentar reenviar un valor-un valor-como, por ejemplo creando una instancia de la forma 2) con lvalue referencia de tipo T, es un error en tiempo de compilación .

Original:

Attempting to forward an rvalue as an lvalue, such as by instantiating the form 2) with lvalue reference type T, is a compile-time error.

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Parámetros

t

-

el objeto a ser reenviado Original: the object to be forwarded The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.

Valor de retorno

static_cast<T&&>(t)

Excepciones

noexcept specification:  

noexcept

  (desde C++11)

Ejemplo

Este ejemplo demuestra el reenvío perfecto del parámetro de la make_unique function () con el argumento del constructor de la clase T

Original:

This example demonstrates perfect forwarding of the parameter of the function make_unique() to the argument of the constructor of class T

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#include <iostream>
#include <memory>
#include <utility>
 
struct A {
    A(int&& n) { std::cout << "rvalue overload, n=" << n << "\n"; }
    A(int& n)  { std::cout << "lvalue overload, n=" << n << "\n"; }
};
 
template<class T, class U>
std::unique_ptr<T> make_unique(U&& u)
{
    return std::unique_ptr<T>(new T(std::forward<U>(u)));
}
 
int main()
{
    std::unique_ptr<A> p1 = make_unique<A>(2); // rvalue
    int i = 1;
    std::unique_ptr<A> p2 = make_unique<A>(i); // lvalue
}

Salida:

rvalue overload, n=2
lvalue overload, n=1

Complejidad

Constant

Original:

Constant

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Ver también

move (C++11)	obtiene una referencia de valor- Original: obtains an rvalue reference The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (plantilla de función)
move_if_noexcept (C++11)	obtiene una referencia de valor-si el constructor movimiento no tira Original: obtains an rvalue reference if the move constructor does not throw The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (plantilla de función)