测试：
$a = [
'a'=>'Tom',
'b'=>'Mary',
'c'=>'Peter',
'd'=>'Jack'
];
$b = [];
foreach ($a as $v) {
$b[] = $v;
}
var_dump($a);
var_dump($b);
结论：
$a: [ ‘a’=>’Tom’,’b’=>’Mary’,’c’=>’Peter’,’d’=>’Jack’]
$b: [ ‘a’=>’Tom’,’b’=>’Mary’,’c’=>’Peter’,’d’=>’Jack’]