英文:
What is meant by the statement: "operator != has been removed in C++20 for std::pair"?
问题
与上面的问题一样。我正在阅读关于std::pair的内容，该内容位于cppreference上，其中写着：
operator==
operator!= // (removed in C++20)
operator< // (removed in C++20)
operator<= // (removed in C++20)
operator> // (removed in C++20)
operator>= // (removed in C++20)
operator<=> // (C++20)
为了验证这一点，我编写了以下代码，在最新的gcc编译器上似乎运行得很完美，而我预期编译器会报语法错误，那么cppreference中写的removed in C++20是什么意思呢？
英文:
Exactly the question above. I was reading about std::pair on cppreference where the following was written:
> cpp
> operator==
> operator!= // (removed in C++20)
> operator< // (removed in C++20)
> operator<= // (removed in C++20)
> operator> // (removed in C++20)
> operator>= // (removed in C++20)
> operator<=> // (C++20)
>
To verify this, I have written the following code, which seems to be running perfectly on the latest gcc compiler, whereas I expected a syntax error from the compiler, so what does cppreference mean by writing removed in C++20 for operator !=?
答案1
得分: 3
线索在于C++20中添加的内容，即<=>操作符。
<=>是_三路比较_操作符，也被称为_飞船_操作符。它的目的是将所有类型的相等比较（<、>=、!=等等）定义为一个单一的函数。
由于其他比较操作符是使用三路比较操作符隐式提供的，因此不再需要单独的操作符实现，它们已被移除。
编辑：
事实证明，我完全错了。a != b并不被重写为使用a <=> b；它被重写为使用!(a == b)；请参见被标记为重复的问题的答案。
英文:
The clue is in what was added in C++20, i.e. the <=> operator.
<=> is the three-way comparison operator, also known as the spaceship operator. Its purpose is to define all types of equality comparisons (<, >=, !=, and so on) as a single function.
Since the other comparison operators are implicitly provided using the three-way comparison operator, the individual operator implementations are no longer needed and have been removed.
EDIT:
Turns out I'm completely wrong here. a != b isn't rewritten to use a <=> b; it's rewritten to use !(a == b); see answer to the question that this is marked as a duplicate of.
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