PHP expression a || b = c

Question

I don't really understand the following expression, what it does and how it works.

a || b = c

I guess it check if a is true, and if it's not, it run b = c?

Exemple of application:

$id || $data['created'] = $now

Answer 1

It's short for:

($id == true) || (($data['created'] = $now) == true)

Factoring in short circuit logic and the fact that the result of the expression itself is ignored:

if (!$id) {
    $data['created'] = $now;
}

See also: Logical operators

Answer 2

In my understanding it means:

a OR the posibility to give b the value of c.

or in your case

$id OR the posibility to give $data['created'] the value of $now