$global = 'hello';
$bbb = function()use($global){
  echo $global."\n";
};
$bbb();
//输出 'hello'

$global = 'hello';
$fun = function(){
  global $global;
  $global =' world';
  echo $global."\n";
};
$fun();
// 输出 'world'

$global = 'hello';
$fun = function(){
  global $global;
  $global =' world';
  echo 'a:'.$global."\n";
};
$ccc = function(){
  echo 'b:'.$global;
};
$fun()
$ccc()
/*

a: world
Notice: Undefined variable: global in xxxxxxx on line xx
*/

<?php
$global = 'hello';
$fun = function(){
  global $global;
  $global ='world';
  echo 'a:'.$global."\n";
};
$bbb = function()use($global){
  $global = 'china';
  echo 'c:'.$global."\n";
};
$fun();
echo 'b:'.$global."\n";
$bbb();
echo 'd:'.$global;

a: world
b: world
c:china
d: world

class Cart
{
  const PRICE_BUTTER = 1.00;
  const PRICE_MILK  = 3.00;
  const PRICE_EGGS  = 6.95;
  protected  $products = array();
  public function add($product, $quantity)
  {
    $this->products[$product] = $quantity;
  }
  public function getQuantity($product)
  {
    return isset($this->products[$product]) ? $this->products[$product] :
      FALSE;
  }
  public function getTotal($tax)
  {
    $total = 0.00;
    $callback =
      function ($quantity, $product) use ($tax, &$total)
      {
        $pricePerItem = constant(__CLASS__ . "::PRICE_" .
          strtoupper($product));
        $total += ($pricePerItem * $quantity) * ($tax + 1.0);
      };
    array_walk($this->products, $callback);
    return round($total, 2);
  }
}
$my_cart = new Cart;
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);
print $my_cart->getTotal(0.05) . "\n";