forward
描述 (Description)
如果arg不是左值引用，则返回对arg的右值引用。
声明 (Declaration)
以下是std :: forward函数的声明。
template <class T> T&& forward (typename remove_reference<T>::type& arg) noexcept;
template <class T> T&& forward (typename remove_reference<T>::type&& arg) noexcept;
C++11
template <class T> T&& forward (typename remove_reference<T>::type& arg) noexcept;
template <class T> T&& forward (typename remove_reference<T>::type&& arg) noexcept;
参数 (Parameters)
arg - 这是一个对象。
返回值 (Return Value)
如果arg不是左值引用，则返回对arg的右值引用。
异常 (Exceptions)
Basic guarantee - 此函数永远不会抛出异常。
数据竞争 (Data races)
没有
例子 (Example)
在下面的例子中解释了std :: forward函数。
#include <utility>
#include <iostream>
void overloaded (const int& x) {std::cout << "[It is a lvalue]";}
void overloaded (int&& x) {std::cout << "[It is a rvalue]";}
template <class T> void fn (T&& x) {
overloaded (x);
overloaded (std::forward<T>(x));
}
int main () {
int a;
std::cout << "calling fn with lvalue: ";
fn (a);
std::cout << '\n';
std::cout << "calling fn with rvalue: ";
fn (0);
std::cout << '\n';
return 0;
}
让我们编译并运行上面的程序，这将产生以下结果 -
calling fn with lvalue: [It is a lvalue][It is a lvalue]
calling fn with rvalue: [It is a lvalue][It is a rvalue]
