如何让PHP避免懒惰求值? [英] How can I have PHP avoid lazy evaluation?

问题描述

关于PHP评估布尔表达式的方式，我有一个有趣的问题.例如，如果有，

I have an interesting question about the way PHP evaluates boolean expressions. When you have, for example,

$expression = $expression1 and $expression2;

或

if ($expression1 and $expression2)

PHP首先检查$expression1的评估结果是否为 true .如果不是这种情况，那么只需跳过$expression2即可避免不必要的计算.在我编写的脚本中，我有:

PHP first checks if $expression1 evaluates to true. If this is not the case, then $expression2 is simply skipped to avoid unnecessary calculations. In a script I am writing, I have:

if ($validator->valid("title") and $validator->valid("text"))

我需要对第二条语句($validator->valid("text"))进行评估，即使第一条语句的评估结果为false.我想问你，是否有一些简单的方法可以强制PHP始终评估这两个语句.谢谢！

I need to have the second statement ($validator->valid("text")) evaluated even if the first one evaluates to false. I would like to ask you whether there is some easy way to force PHP to always evaluate both statements. Thank you!

推荐答案

这称为短路评估，为避免这种情况，您需要使用单个&:

This is known as short circuit evaluation, and to avoid it you need to do this, using a single &:

if($validator->valid("title") & $validator->valid("text")) {

}

请注意，这不是使用逻辑运算符，而是实际上是

Note that this is not using logical operators but actually bitwise operators:

它们是对数字的二进制表示起作用的运算符.在不先将逻辑值分别转换为数字1和0的情况下，它们不会将逻辑值(即"true"或"false")作为参数.它们也不返回逻辑值，而是数字.当然，您以后可以将这些数字视为逻辑值(在这种情况下，0强制转换为"false"，其他所有强制转换为"true")，但这是PHP的类型强制转换规则的结果，无需执行任何操作与操作员的行为有关.

They're operators that act on the binary representations of numbers. They do not take logical values (i.e., "true" or "false") as arguments without first converting them to the numbers 1 and 0 respectively. Nor do they return logical values, but numbers. Sure, you can later treat those numbers as though they were logical values (in which case 0 is cast to "false" and anything else is cast to "true"), but that's a consequence of PHP's type casting rules, and nothing to do with the behavior of the operators.

因此，关于使用这种副作用规避短路评估是否是一种好习惯，存在一些争议.我个人至少要评论一下&是有意的，但是如果您想变得尽可能纯正，则应该先评估它们是否有效，然后再执行if.

As such, there is some debate as to whether it is good practice to use this side effect to circumvent short-circuit evaluation. I would personally at least put a comment that the & is intentional, but if you want to be as pure as possible you should evaluate whether they are valid first and then do the if.

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