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run code in 200+ php & hhvm versions
Bugs & Features
<?php var_dump(key(array_flip(array('foo' => 'bar'))));
Output for 4.3.0 - 5.0.4, 5.1.0 - 5.6.30, hhvm-3.10.1 - 3.17.3, 7.0.0 - 7.2.0
string(3) "bar"
Output for 5.0.5
Fatal error: Only variables can be passed by reference in /in/8I6dd on line 2
Process exited with code 255.