PHP惰性布尔评估 [英] PHP Lazy Boolean Evaluation

问题描述

因此，我有一个条件语句:

I have a conditional statement thus:

if($boolean && expensiveOperation()){ ...}

PHP是否具有懒惰的布尔值评估，即它将检查$boolean，并且如果它为false，则不必费心执行昂贵的操作?如果是这样，我应该按什么顺序放置变量?

Does PHP have lazy boolean evaluation, i.e. will it check $boolean and if it is false not bother performing the expensive operation? If so, what order should I put my variables?

推荐答案

是的.这称为短路评估.请参阅文档页面上的评论 ...

Yes it does. It's called short-circuit evaluation. See the comments on the documentation page...

至于订单，它根据操作员执行检查优先，然后从左到右.所以:

As for the order, it performs the checks based on Operator Precedence and then left to right. So:

A || B || C

首先将评估A，然后仅在A为假时才评估B，仅在A和B都为假时才评估C ...

Will evaluate A first, and then B only if A is false, and C only if both A and B are false...

但是

A AND B || C

将始终评估B || C，因为||的优先级高于AND(对于&&而言并非如此).

Will always evaluate B || C, since || has a higher precedence than AND (not true for &&).

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