elseif与else if之间的根本区别 [英] underlying difference between elseif vs else if

问题描述

我想知道elseif和else if之间的区别.

I was wondering the differnce between elseif and else if.

我正在阅读手册，其中指出是否使用括号{}它们的用法相同，但是不使用花括号时，只有elseif起作用.

I was reading the manual which says if using the braces {} they are treated the same but only elseif works when not using the braces.

另一位贡献者说:

请注意} elseif(){比} else if(){

Note that } elseif() { is somewhat faster than } else if() {

他用基准测试对其进行了备份.

and he backed it up with a benchmark test.

在我看来，elseif是说它和说:的真正方法.

To me it seems like elseif is the true way of saying it and saying:

else if() {...}

确实等同于:

else { if() {...} }

这可能解释了为什么它稍微慢一些.

which might explain why its marginally slower.

我习惯使用else if，因为那也是我用其他语言编写的方式.我真的不认为键入哪种方式很重要(除非您不使用花括号..但我认为无论如何都使用花括号总是很好的)，我只是对底层的细节感到好奇.

I am used to using else if because thats how I do it in other languages as well. I don't really think it matters which way you type it (unless you are not using braces.. but I think its always good to use braces anyways) I was just curious about the underlying details.

我正确吗?

推荐答案

除了我的评论，从PHP源码中可以看到，唯一提高速度的是PHP的解析器为elseif提供了特殊标记，毫不奇怪地称为T_ELSEIF.但是我敢肯定，提高速度无非是在替代语法中允许elseif的副作用:

In addition to my comment, from what I can see in the PHP source, the only speed boost is that PHP's parser has a special token for elseif, unsurprisingly known as T_ELSEIF. But I'm sure the speed boost is nothing more than a side effect of allowing elseif in the alternative syntax:

if (cond1):
    // Do something
elseif (cond2):
    // Do something else
else:
    // Do something else
endif;

类似于Python，它使用elif，else if和空格，而不必不必要地使解析器的实现代码复杂化(即在看到冒号和if关键字之间采取不同的动作).因此，分别在else和if之后分别需要一个冒号，这就是语言规则的规定.

Similar to Python, which uses elif, else if with a space wouldn't be allowed without having to unnecessarily complicate the parser's implementation code (i.e. to act differently between seeing a colon and the if keyword). So a colon is required directly after else and if respectively, and that's how the language rule is stipulated.

Ergo，我很确定PHP会将else if视为单语句else中的条件块.

Ergo I'm pretty sure PHP just treats else if as a conditional block in a singular-statement else.

如果所有速度差异 ，都应将其归咎于解析器.

If there are any speed differences at all, blame the parser for most of them.

这篇关于elseif与else if之间的根本区别的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！