3v4l.org

run code in 200+ PHP versions simultaneously
<?php $var = array( 'a' => 'a', 'b' => 'b', ); array_walk($var, function ($value) { }); var_dump(key($var));
based on 9bk3a
Output for 5.3.0 - 5.3.13, 5.4.0 - 5.4.3, 7.1.0 - 7.4.6
string(1) "a"
Output for 5.3.14 - 5.3.29, 5.4.4 - 7.0.31
NULL
Output for 4.4.2 - 4.4.9, 5.1.0 - 5.2.17
Parse error: syntax error, unexpected T_FUNCTION in /in/46Cbn on line 8
Process exited with code 255.
Output for 4.3.0 - 4.3.1, 4.3.5 - 4.4.1, 5.0.0 - 5.0.5
Parse error: parse error, unexpected T_FUNCTION in /in/46Cbn on line 8
Process exited with code 255.
Output for 4.3.2 - 4.3.4
Parse error: parse error in /in/46Cbn on line 8
Process exited with code 255.