c++ - 在 MoveAssignable 的情况下，标准对 self 移动赋值有何看法？

Question

这是 C++17 的 current description MoveAssignable 的:

t = rv;

If t and rv do not refer to the same object, t is equivalent to the value of rv before the assignment rv's state is unspecified. [ Note: rv must still meet the requirements of the library component that is using it, whether or not t and rv refer to the same object. The operations listed in those requirements must work as specified whether rv has been moved from or not. — end note ]

“rv 仍必须满足正在使用它的库组件的要求”指的是什么？

如果 t 和 rv 指的是同一个对象怎么办？在这种情况下，具有 MoveAssignable 的类型可以/应该做什么？

描述的意思是:

1. 库根本不会用 self 调用移动赋值，所以在这种情况下类型可以做任何它想做的事(甚至崩溃)

2. 或者类型应该以某种方式处理这种情况(不允许崩溃)，但它的结果并不重要

3. 还是别的？

注意:这里有类似的问题，但有冲突/旧的(C++14 有不同的规则)答案、评论，所以我想澄清一下。

Answer 1

What does "rv must still meet the requirements of the library component that is using it" refer to?

这是一种迂回的说法，即即使 rv 的状态未指定，它也必须是一个有效状态。例如，记录“我走了!”的类型。如果赋值是需要支持的操作之一，则不允许为后续的重新赋值声明和抛出异常。

What if t & rv refer to the same object?

您已经引用了答案:“rv 的状态未指定。”这与 t 是否指代同一对象无关。

Does the description mean:

2. or the type should handle this case somehow (no crashing allowed), but its result doesn't matter

是的，这个，差不多。