这是转发参考吗? [英] Is this a forwarding reference?

问题描述

在此示例中，斯科特·迈耶斯(Scott Meyers)明确阐明了右值引用和转发引用之间的区别:

The distinction between rvalue references and forwarding references was made clear enough in this example by Scott Meyers:

Widget&& var1 = someWidget;     // here, "&&" means rvalue reference (1)

auto&& var2 = var1;             // here, "&&" does not mean rvalue reference (2)

template<typename T>
void f(std::vector<T>&& param); // here, "&&" means rvalue reference (3)

template<typename T>
void f(T&& param);              // here, "&&"does not mean rvalue reference (4)

本质上，当我们有一个可推论的上下文时就发生了区分，因此情况(3)明确指出我们有一个vector<...>&&，而要推论情况(4)的T，并且(在应用参考折叠规则之后)按值类别"分类.

Essentially the distinction happens when we have a deducible context, hence case (3) explicitly states that we have a vector<...>&& whereas the T in case (4) is to be deduced and (after applying reference collapsing rules) categorized in terms of "value category".

但是，模式匹配稍微复杂一点会怎样?以下面的情况为例:

template <template <class...> class Tuple, class... Ts>
void f(Tuple<Ts...>&& arg)
{

}

&&在这里是什么意思?

What does && mean here ?

推荐答案

在最后一个示例中，arg是右值引用.

In your last example, arg is an rvalue reference.

转发参考是对cv不合格模板参数的右值参考

A forwarding reference is an rvalue reference to a cv-unqualified template parameter

和Tuple<Ts...>不是模板参数.

(来自[temp.deduct.call]的引用.)

(Citation from [temp.deduct.call].)

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