问题
Sorry if this sounds like a really silly question.
But I Googled the web and also Googled specifically both the php.net site and the stackoverflow.com site.
I know PHP does short circuit lazy evaluation when using and, or, &&, || operators, but where is it stated loud and clear in the PHP manual???
I found only Wikipedia as the only \'trusted\' source that say PHP does lazy evaluation on these operators.
回答1:
Closest thing I can find to an 'official' mention of PHP's short-circuit implementation: http://php.net/manual/en/language.operators.logical.php
回答2:
This is not an uncommon feature of expression evaluation. The PHP manual page on logical operators makes a passing reference to it in one of the illustrative examples though.
Short circuit evaluation is a commonly exploited idiom, and you can rely on its continued support in the language, otherwise vast amounts of code would break!
来源：https://stackoverflow.com/questions/3220919/php-short-circuit-lazy-evaluation-where-is-it-in-the-php-net-manual