实际描述

• 文件路径：例如，book/zh-cn/02-usability.md
• 原文段落：

将亡值(xvalue, expiring value)，是 C++11 为了引入右值引用而提出的概念（因此在传统 C++中，纯右值和右值是同一个概念），也就是即将被销毁、却能够被移动的值。

将亡值可能稍有些难以理解，我们来看这样的代码：
std::vector<int> foo() {
    std::vector<int> temp = {1, 2, 3, 4};
    return temp;
}

std::vector<int> v = foo();

原文解释如下
http://naipc.uchicago.edu/2015/ref/cppreference/en/cpp/language/value_category.html
A function call expression, if the function's return type is an rvalue reference to object type, such as std::move(val)
A cast expression to an rvalue reference to object type, such as static_cast<T&&>(val) or (T&&)val
a non-static class member access expression, in which the object expression is an xvalue
A pointer-to-member expression in which the first operand is an xvalue and the second operand is a pointer to data member.

将亡值可能稍有些难以理解，我们来看这样的代码：
std::vector<int> foo() {
    std::vector<int> temp = {1, 2, 3, 4};
    return std::move(temp);
}

std::vector<int> v = foo();

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