PHP - if语句中的颠倒顺序 [英] PHP - reversed order in if statement

问题描述

这是一个问题，这让我很长时间，并找不到任何答案...
注意到它被很多Zend Framework开发人员使用，

This is a question that is bugging me for a long time and can't find any answer... Noticed it's used quite a lot by Zend Framework Developers,

以下2个if语句有什么区别？ ：

What is the difference between following 2 "if" statements? :

if (null === $this->user) { ... }

if ($this->user === null) { ... }

第一个看起来很奇怪;]

To me the first one looks kinda odd ;]

感谢回答。

推荐答案

p>这不是你的脚本工作方式的区别，它只是一个编码标准，一个建议

This is not a difference for the way your script works, it's just a coding standard, a recommendation

推荐使用它的原因是这样的： / p>

The reason why it is recommended to use it this way:

if (null == $this->user)

是这样的事实，如果你输入错误，而不是==，你会得到一个错误，而

is the fact that if you mistype and write = instead of == you will get an error, while

($this->user = null)

($this->user == null)

有效，但会导致奇怪的错误（赋值和最终值被计算为bool而不是比较）

works but causes weird bugs (assignment and the final value is evaluated as bool instead of comparison)

猜测它只是作为一个习惯扩展为严格的比较运算符（===）

and I guess it just extended as a habit to the strict comparison operator (===)

更新：因为我看到还有一些活动这个线程甚至3年后我发布的答案，我想我会添加一些我忘了提到。这种类型的符号称为 yoda条件，您可以在此维基百科页面。

Update: since I see that there's still some activity on this thread even 3 years after I posted the answer I figured I would add something I forgot to mention. This type of notation is known as yoda conditions, you can read more about it on this wikipedia page for example.

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