Clarify on PHP operators precedence ! and =

April 3, 2023

I was happy coding until I wrote a code like this (in PHP 8.2):

if (!$a = false) {
    echo '$a is false';
}

This snippet will print $a is false as expected. But according to the PHP documentation, the ! operator has greater precedence over the = operator, so that should be interpreted as (!$a) = null which I know is wrong, but hence my question: why? Is there a "hack" to allow this? Do I’m missing some documentation?

It make sense with instanceof:

$object = 'foo';
if (!$object instanceof SomeUnexistentClass) {
    echo '$object is not instance of SomeUnexistentClass)';
}

That code will execute the echo because instanceof has greater precedence over the ! operator. So why the former code is valid?

>Solution :

There’s a note in the docs:

Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.