What does this mean? - if (null === ($bar = $foo->getBar()))

When we have something like:

开发者_如何学Cif (null === ($bar = $foo->getBar())) {

}

Are we doing three things on this single line ? Are we:

1) Declaring a variable.

2) Attribute that variable a value.

3) Check if that variable value is null.

?

Yup, exactly like:

$bar = $foo->getBar();
if (null === $bar) {

}

$bar will receive the value returned by $foo->getBar(), and then the expression tests whether that (the result of the assignment expression, which is the value that got assigned to $bar) is === null. (And if this is the first use of $bar, then it's creating a new variable.)

First you execute function getBar() which returns something what is assigned to variable $bar. Then operator === returns true if $bar is equal to null and they are the same type (null type).

http://www.php.net/manual/en/language.operators.comparison.php

http://www.php.net/manual/en/language.types.null.php

it's equal to:

 $bar = $foo->getBar();
 if ($bar === null) {

 }

Keep in mind that there is difference between === and ==. === is exact comparison operator, so 0 ==null is true but 0 === null is false. "" == null is true, "" === null is false.