$a = function() use($b) {}

function callback($fun) {
$fun();
}
$msg = "Hello, everyone";
$fun = function () use($msg) {
print "This is a closure use string value, msg is: $msg. <br />/n";
};
$msg = "Hello, everybody";
callback($fun);

/** 
 * 一个利用闭包的计数器产生器 
 * 这里其实借鉴的是python中介绍闭包时的例子... 
 * 我们可以这样考虑: 
 *      1. counter函数每次调用, 创建一个局部变量$counter, 初始化为1. 
 *      2. 然后创建一个闭包, 闭包产生了对局部变量$counter的引用. 
 *      3. 函数counter返回创建的闭包, 并销毁局部变量, 但此时有闭包对$counter的引用,  
 *          它并不会被回收, 因此, 我们可以这样理解, 被函数counter返回的闭包, 携带了一个游离态的 
 *          变量. 
 *      4. 由于每次调用counter都会创建独立的$counter和闭包, 因此返回的闭包相互之间是独立的. 
 *      5. 执行被返回的闭包, 对其携带的游离态变量自增并返回, 得到的就是一个计数器. 
 * 结论: 此函数可以用来生成相互独立的计数器. 
 */  
function counter() {  
    $counter = 1;  
    return function() use(&$counter) {return $counter ++;};  
}  
$counter1 = counter();  
$counter2 = counter();  
echo "counter1: " . $counter1() . "<br />/n";  
echo "counter1: " . $counter1() . "<br />/n";  
echo "counter1: " . $counter1() . "<br />/n";  
echo "counter1: " . $counter1() . "<br />/n";  
echo "counter2: " . $counter2() . "<br />/n";  
echo "counter2: " . $counter2() . "<br />/n";  
echo "counter2: " . $counter2() . "<br />/n";  
echo "counter2: " . $counter2() . "<br />/n";  
?>

<?php
// 一个基本的购物车，包括一些已经添加的商品和每种商品的数量。
// 其中有一个方法用来计算购物车中所有商品的总价格。该方法使用了一个closure作为回调函数。
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);
            };

        //使用用户自定义函数对数组中的每个元素做回调处理
        array_walk($this->products, $callback);
        return round($total, 2);;
    }
}
 
$my_cart = new Cart;
 
// 往购物车里添加条目
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);
 
// 打出出总价格，其中有 5% 的销售税.
print $my_cart->getTotal(0.05) . "\n";
// The result is 54.29
?>

function html($code , $id="", $class=""){
if ($id !== "") $id = " id = \"$id\"" ;
$class = ($class !== "")? " class =\"$class\">":">";
$open = "<$code$id$class";
$close = "</$code>";
return function ($inner = "") use ($open, $close){
return "$open$inner$close";
    };
}

<?php
$fib = function($n) use(&$fib) {
    if($n == 0 || $n == 1) return 1;
    return $fib($n - 1) + $fib($n - 2);
};
 
echo $fib(2) . "\n"; // 2
$lie = $fib;
$fib = function(){die('error');};//rewrite $fib variable 
echo $lie(5); // error   because $fib is referenced by closure

<?php
$recursive = function () use (&$recursive){
// The function is now available as $recursive
}

<?php
$result = 0;
 
$one = function()
{
    var_dump($result);
};
 
$two = function() use ($result)
{
    var_dump($result);
};
 
$three = function() use (&$result)
{
    var_dump($result);
};
 
$result++;
 
$one();    // outputs NULL: $result is not in scope
$two();    // outputs int(0): $result was copied
$three();    // outputs int(1)