3v4l.org

run code in 300+ PHP versions simultaneously
<?php $foo = function() { return null; }; echo (int)isset( $foo ); // TRUE because you're testing $foo echo '-'; echo (int)isset( $foo() ); // FALSE because you're testing $foo's response
Output for 7.0.0 - 7.0.1
Fatal error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead) in /in/aaeQQ on line 8
Process exited with code 255.
Output for 5.5.24 - 5.5.30, 5.6.8 - 5.6.16
Fatal error: Cannot use isset() on the result of a function call (you can use "null !== func()" instead) in /in/aaeQQ on line 8
Process exited with code 255.
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