Is this PHP syntax correct?

Question

I am currently studying ZEND framework and came across this in index.php:

// Define path to application directory
defined('APPLICATION_PATH')
    || define('APPLICATION_PATH', realpath(dirname(__FILE__) . '/../application'));

Is this the same as this?

if(!defined('APPLICATION_PATH')){
    define('APPLICATION_PATH', realpath(dirname(__FILE__) . '/../application'));
}

I have never came across this type of shorthand syntax before.

Answer 1

|| is a short-circuit operator which means that the second operand, in this case define(...) is only evaluated in case the first operand evaluates to false. Because operands to shirt-circuit operators may actually have side effects as is your case, short-circuiting may substitute an if statement.

Check this article: http://en.wikipedia.org/wiki/Short-circuit_evaluation

Answer 2

Functionally, yes, it is the same. The defined function returns a boolean, so it uses short-circuit evaluation to mean "either this is defined, OR execute this definition."