std::forward

Questa pagina è stata tradotta in modo automatico dalla versione in ineglese della wiki usando Google Translate. La traduzione potrebbe contenere errori e termini strani. Muovi il puntatore sopra al testo per vedere la versione originale. Puoi aiutarci a correggere gli gli errori. Per ulteriori istruzioni clicca qui. Click here for the English version of this page

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

• Se una chiamata a wrapper() passa un std::string rvalue, quindi T si deduce a std::string (non std::string&, const std::string& o std::string&&), e std::forward assicura che un riferimento rvalue viene passato 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.

  The text has been machine-translated via Google Translate.
  You can help to correct and verify the translation. Click here for instructions.
• Se una chiamata a wrapper() passa un const lvalue std::string, quindi T si deduce a const std::string&, e std::forward assicura che un const lvalue riferimento viene passato al 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.

  The text has been machine-translated via Google Translate.
  You can help to correct and verify the translation. Click here for instructions.
• Se una chiamata a wrapper() passa un non-const std::string lvalue, quindi T si deduce a std::string&, e std::forward assicura che un riferimento non const lvalue viene passato al 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.

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

[modifica] Note

[modifica] Parametri

[modifica] Valore di ritorno

static_cast<T&&>(t)

[modifica] Eccezioni

[modifica] Esempio

#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
}

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

[modifica] Complessità

[modifica] Vedi anche