一个php语法的问题

看到一个代码不懂什么意思，求大神解答
foreach($GLOBALS AS $_k=>$_v) {
${$_k} = $_v;
}

[code="php"]
foreach($GLOBALS AS $_k=>$_v) {
${$_k} = $_v;
}
[/code]
${$_k} 可变变量
这时说的很清楚[url]http://www.php.net/manual/zh/language.variables.variable.php[/url]

php foreach 用法

<?php
class MyClass
{
public $var1 = 'value 1';
public $var2 = 'value 2';
public $var3 = 'value 3';

protected $protected = 'protected var';
private   $private   = 'private var';

function iterateVisible() {
   echo "MyClass::iterateVisible:\n";
   foreach($this as $key => $value) {
       print "$key => $value\n";
   }
}

}

$class = new MyClass();

foreach($class as $key => $value) {
print "$key => $value\n";
}
echo "\n";

$class->iterateVisible();

?>

The above example will output:

var1 => value 1
var2 => value 2
var3 => value 3

MyClass::iterateVisible:
var1 => value 1
var2 => value 2
var3 => value 3
protected => protected var
private => private var

学习了，我php打酱油的