empty as an empty condition

/ * * 
 * Empty as an empty conditions: 
 * (1) "" (the empty string) 
 * (2) 0.001 (as an integer of 0) 
 * (3) .0.0 (as float 0) 
 * ( 4) "0" (as string 0) 
 * (. 5) .NULL 
 * (. 6) .FALSE 
 * (. 7) .Array () (an empty array) 
 * (. 8) $ var;. (a declared , but there is no value of the variable) 
 * / 
var_dump ( empty ( "" ));
 var_dump ( empty (0 ));
 var_dump ( empty (0.0 ));
 var_dump ( empty ( "0" ));
 var_dump ( empty ( NULL ) );
 var_dump ( empty (FALSE));
var_dump(empty(array()));
$foo;
var_dump(empty($foo));