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<?php $key = ''; $arr = array('' => array('foo', 1)); var_dump($arr, $key, $arr[$key]);
Output for 4.3.0 - 7.1.0
array(1) { [""]=> array(2) { [0]=> string(3) "foo" [1]=> int(1) } } string(0) "" array(2) { [0]=> string(3) "foo" [1]=> int(1) }