为什么在C ++ 20中std :: move没有[[nodiscard]]? [英] Why is std::move not [[nodiscard]] in C++20?

问题描述

我最近阅读了C ++ 17中的[[nodiscard]]，据我了解，它是一项新功能(按合同设计?)，它迫使您使用返回值.对于像std::launder这样的有争议的函数(自C ++ 20起不丢弃)，这是有道理的，但是我不知道为什么std::move的定义没有像C ++ 17/20中那样.您知道很好的理由还是因为C ++ 20尚未完成?

I've recently read about [[nodiscard]] in C++17, and as far as I understand it's a new feature (design by contract?) which forces you to use the return value. This makes sense for controversial functions like std::launder (nodiscard since C++20), but I wonder why std::move isn't defined like so in C++17/20. Do you know a good reason or is it because C++20 isn't finalised yet?

推荐答案

AFAIK

AFAIK P0600R1 is the only proposal for adding [[nodiscard]] to the standard library that was applied to C++20. From that paper:

我们建议采取保守的方法:

We suggest a conservative approach:

[...]

在以下情况下不应添加:

It should not be added when:

• [...]
• 不使用返回值没有意义，但不会造成伤害，并且通常不是错误
• [...]

• [...]
• not using the return value makes no sense but doesn’t hurt and is usually not an error
• [...]

因此，[[nodiscard]]不应发出错误的代码

So, [[nodiscard]] should not signal bad code if this

• [...]
• 没有受到伤害，并且可能没有状态改变就意味着不会发生

因此，原因是标准库使用的是保守方法，而尚未提出更具综合性的方法.

So the reason is that the standard library uses a conservative approach and a more aggresive one is not yet proposed.

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