3v4l.org

run code in 150+ php & hhvm versions
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<?php $x=array('a'=>null); var_dump(isset($x['a']), array_key_exists('a', $x));
Output for 4.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
bool(false) bool(true)