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<?php enum ArrayKeys { case IncludeAll; } $array = [ 'empty' => '', 'enum' => ArrayKeys::IncludeAll, 'zero' => 0, 'one' => 1, 'null' => null, 'false' => false, 'true' => true, ]; var_export(array_keys($array, ArrayKeys::IncludeAll));
Output for 8.5.0 - 8.5.3
array ( 0 => 'enum', 1 => 'true', )
Output for 8.1.0 - 8.1.34, 8.2.0 - 8.2.30, 8.3.5 - 8.3.30, 8.4.1 - 8.4.18
array ( 0 => 'enum', )
Output for 8.0.1 - 8.0.29
Parse error: syntax error, unexpected identifier "ArrayKeys" in /in/5Br1a on line 3
Process exited with code 255.

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