PHP why (null === $variable) and not ($variable === null) in comparison?

Question

When reading Symfony2 code I came across this comparaison many times

if (null === $variable ) { ... }

I use

if ($variable === null ){ ... }

because I see it more readable.

Is there a wisdom behind using the first notation ?

Answer 1

No compile/interpretting difference at all, it's pure code style.
It's also known as Yoda Conditions.

Answer 2

It helps prevent accidental assignments:

if ($foo = null) { ... }

would not cause a parse error, while will

if (null = $foo) { ... }

1st example: http://sandbox.onlinephpfunctions.com/code/fff14c285a18a7972a3222ff5af08da825760c10 2nd example: http://sandbox.onlinephpfunctions.com/code/118d494c17381d8e129ba005465bf84d9b8819bd

Answer 3

Not only does it help prevent accidental assignments, but also avoids confusion when we do intentionally want to make an assignment when evaluating a condition.

if (null !== $article = $repository->findOneById($request->query->get('id'))) {
    $title = $article->getTitle();

    //....
}