is_null($ x)vs $ x ===在PHP中为null [英] is_null($x) vs $x === null in PHP
问题描述
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What's the difference between is_null($var) and ($var === null)?
PHP有两个(据我所知，如果您计算isset()则为三个)方法来确定值是否为空:is_null()和=== null.我听说过但未确认=== null更快，但是在代码审查中，有人强烈建议我使用is_null()代替，因为它是专门为null评估目的而设计的.他还开始谈论数学之类的东西.
PHP has two (that I know of, and three if you count isset()) methods to determine if a value is null: is_null() and === null. I have heard, but not confirmed, that === null is faster, but in a code review someone strongly suggested that I use is_null() instead as it is specifically designed for the null-evaluation purpose. He also started talking about math or something.
无论如何，is_null()显然更慢的事实也使我相信它的作用比=== null还要多，并且可能是首选.有任何理由使用其中之一吗?总是首选吗?那isset()呢?
Anyway, the fact that is_null() is apparently slower also leads me to believe that it's doing more than === null does and is probably preferred. Is there any reason to use one or the other? Is one always preferred? What about isset()?
作为可能无法解决此问题的附录，isset()与is_null()呢?似乎所有isset()都将取消显示通知，因此，除非您实际上想要未定义变量的通知，否则有理由使用is_null()吗?如果您知道变量当时已初始化怎么办?
As an addendum to possibly not get this question closed, what about isset() vs. is_null()? It seems that all isset() will do is suppress the notice, so unless you actually want a notice for an undefined variable, any reason to use is_null() instead? How about if you know the variable is initialized at the time?
最后，有什么数学理由更喜欢is_null()而不是=== null吗?关于null无法比较的东西?
Finally, is there any mathematical reason to prefer is_null() over === null? Something about null not being comparable?
推荐答案
is_null和=== null之间的功能上没有 完全没有 .
There is absolutely no difference in functionality between is_null and === null.
唯一的区别是is_null是一个函数，因此
The only difference is that is_null is a function and thus
- 稍微慢一点(函数调用开销)
- 可用作回调，例如
array_map('is_null', $array).
我个人会尽可能使用null ===，因为它与false ===和true ===检查更加一致.
Personally, I use null === whenever I can, as it is more consistent with false === and true === checks.
如果需要，可以检查代码: is_identical_function (===)和 php_is_type (is_null)对于IS_NULL情况也做同样的事情.
If you want, you can check the code: is_identical_function (===) and php_is_type (is_null) do the same thing for the IS_NULL case.
相关的isset()语言构造在进行null检查之前检查变量是否确实存在.因此isset($undefinedVar)不会发出通知.
The related isset() language construct checks whether the variable actually exists before doing the null check. So isset($undefinedVar) will not throw a notice.
还请注意，即使值是null，isset()有时也可能返回true-这种情况适用于重载对象，即，如果对象定义了offsetExists/__isset即使偏移量为null的方法也返回true(这实际上很常见，因为人们在offsetExists/__isset中使用array_key_exists).
Also note that isset() may sometimes return true even though the value is null - this is the case when it is used on an overloaded object, i.e. if the object defines an offsetExists/__isset method that returns true even if the offset is null (this is actually quite common, because people use array_key_exists in offsetExists/__isset).
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