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<?php $x = array('12' => 34); var_dump($x); var_dump(gettype(key($x))); var_dump(array_key_exists(true, $x)); var_dump(array_key_exists(12, $x)); var_dump(array_key_exists('12', $x)); var_dump(array_key_exists(12.0, $x));
Output for 4.3.2 - 7.1.7, 7.1.20 - 7.2.6
array(1) { [12]=> int(34) } string(7) "integer" Warning: array_key_exists(): The first argument should be either a string or an integer in /in/SHI79 on line 7 bool(false) bool(true) bool(true) Warning: array_key_exists(): The first argument should be either a string or an integer in /in/SHI79 on line 10 bool(false)
Output for 7.1.10

Process exited with code 137.
Output for 4.3.0 - 4.3.1
array(1) { [12]=> int(34) } string(7) "integer" Warning: array_key_exists() [http://www.php.net/function.array-key-exists]: The first argument should be either a string or an integer in /in/SHI79 on line 7 bool(false) bool(true) bool(true) Warning: array_key_exists() [http://www.php.net/function.array-key-exists]: The first argument should be either a string or an integer in /in/SHI79 on line 10 bool(false)