函数参数为数组时传值、传址的区别，请高手结合实例讲解

$json = '[{"id":27,"children":[{"id":30,"children":[{"id":31}]}]},{"id":28,"children":[{"id":29}]},{"id":32}]';
$arry = json_decode($json,true);
print_r($arry);
echo"
";
print_r(foo($arry));
echo"
";
function foo($ar, $level=0, $parent=0,&$res=array()) {
foreach($ar as $v) {
$t = array();
$v['level'] = $level;
$v['parent'] = $parent;
if(isset($v['children'])) {
$t = $v['children'];
unset($v['children']);
}
$res[] = $v;
if($t) foo($t, $level+1, $v['id'], $res);
}
return $res;
}
?>
Array ( [0] => Array ( [id] => 27 [children] => Array ( [0] => Array ( [id] => 30 [children] => Array ( [0] => Array ( [id] => 31 ) ) ) ) ) [1] => Array ( [id] => 28 [children] => Array ( [0] => Array ( [id] => 29 ) ) ) [2] => Array ( [id] => 32 ) )

Array ( [0] => Array ( [id] => 27 [level] => 0 [parent] => 0 ) [1] => Array ( [id] => 30 [level] => 1 [parent] => 27 ) [2] => Array ( [id] => 31 [level] => 2 [parent] => 30 ) [3] => Array ( [id] => 28 [level] => 0 [parent] => 0 ) [4] => Array ( [id] => 29 [level] => 1 [parent] => 28 ) [5] => Array ( [id] => 32 [level] => 0 [parent] => 0 ) )

如果是这样
function foo($ar, $level=0, $parent=0, $res=array()) {
foreach($ar as $v) {
$t = array();
$v['level'] = $level;
$v['parent'] = $parent;
if(isset($v['children'])) {
$t = $v['children'];
unset($v['children']);
}
$res[] = $v;
if($t) foo($t, $level+1, $v['id'], $res);
}
return $res;
}
结果 则为：
Array ( [0] => Array ( [id] => 27 [level] => 0 [parent] => 0 ) [1] => Array ( [id] => 28 [level] => 0 [parent] => 0 ) [2] => Array ( [id] => 32 [level] => 0 [parent] => 0 ) )
请高手结合此实例，讲解下 传值、传址的区别，谢谢。

回复讨论(解决方案)

值传递：
拷贝一份原始数据进行操作，不改变原值。
引用传递：
操作原始数据，操作过后原始数据会改变。

数组值传递实例代码：output:array(2) {  [0]=>  string(1) "a"  [1]=>  string(1) "b"}数组引用传递outpout:array(1) {  [0]=>  string(2) "dd"}

参考这个看看吧：http://www.cnblogs.com/zcy_soft/archive/2011/12/10/2283570.html

$res[] = $v;
if($t) foo($t, $level+1, $v['id'], $res)
----这两个语句在函数 foo 内部，但原理是一样的。如同楼上所举的例子

传值不会影响原数组，传地址会。
例子：
地址引用

输出：
Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 )

传值

输出：
Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 )
Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 )

说白了就是，函数的参数，默认都是复制一份的，这样你函数内怎么折腾都不会影响到使用函数时传过来的变量
加上&就不会复制，而直接用了

传值就是多复制一份，相互不影响
引用就是同时操作同一份数据，相互影响