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<?php function mutabledefault($arg=array("xyz")) { var_dump($arg); $arg["foo"] = "new"; var_dump($arg); } mutabledefault(); mutabledefault();
Output for 4.3.0 - 5.6.28, hhvm-3.10.0 - 3.12.0, 7.0.0 - 7.1.0
array(1) { [0]=> string(3) "xyz" } array(2) { [0]=> string(3) "xyz" ["foo"]=> string(3) "new" } array(1) { [0]=> string(3) "xyz" } array(2) { [0]=> string(3) "xyz" ["foo"]=> string(3) "new" }