const float& x = something; //认为有害？ [英] const float & x = something; // considered harmful?

问题描述

有一些代码如下：

  //方便在以下代码中使事情更清晰
 const float& x = some.buried.variable.elsewhere; 
 
 //继续在计算中使用x ... 
  

已被告知，const float&是坏，应该只是一个普通的浮点或const浮点。

然而，我不能想到一个令人信服的理由，除了你不必类型'&'。

事实上，在某些情况下，原来可能更好，因为编译器可能不会分配额外的堆栈空间给变量。

换句话说，最初我可以有效地说：

  assert（& x ==& some.buried.variable.elsewhere）
  

此外，在我看来，原来似乎更好地沟通意图，因为引用的整个点是将一个别名替换为另一个值。 / p>

任何人都可以告诉我们const float&版本比一个简单的float或const float更有效？

解决方案

const float& 会优于 const float 。

如果你担心副本是否生效（这与原始类型无关，例如 float ），或者您希望能够在所有共享引用的实例（与 const 成员无关）中更新值。

除此之外，成员中的引用在初始化时是一个巨大的痛苦，所以他们必须提供一个显着的优势，以便有用的替代品，显然不是 const float 的情况。

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* FQA对参考文献总是有趣和引人注目的

There was some code like this:

// Convenience to make things more legible in the following code
const float & x = some.buried.variable.elsewhere;

// Go on to use x in calculations...

I have been told that the "const float &" is "bad" and should just be a plain float or const float.

I, however, could not think of a compelling reason other than "you don't have to type '&'".

In fact, it seems to me that in some cases the original could be better, since compiler might not allocate extra stack space to the variable.

In other words, originally I could validly say:

assert(&x == &some.buried.variable.elsewhere)

Whereas in the second case I cannot.

Also, the original seems to communicate intent better, in my view, since the whole point of a reference is to make an alias to another value.

Can anyone give me examples of where the "const float &" version is worse than a plain "float" or "const float" in some tangible way?

解决方案

I can't think of a reason why const float & would be better than const float.

References make sense if you're either worried about copies being made (which is irrelevant with a primitive type like float) or you want to be able to update a value across all instances that share the reference (which is irrelevant with const members).

On top of that, references in members are a huge pain in the neck* when it comes to initialization, and so they'd have to offer a significant advantage of the alternatives in order to be useful, and it's clearly not the case with const float.

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* The FQA on references is always amusing and thought provoking

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