$a = function() use($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);

/**
 * 一個(gè)利用閉包的計(jì)數(shù)器產(chǎn)生器
 * 這里其實(shí)借鑒的是python中介紹閉包時(shí)的例子...
 * 我們可以這樣考慮:
 *      1. counter函數(shù)每次調(diào)用, 創(chuàng)建一個(gè)局部變量$counter, 初始化為1.
 *      2. 然后創(chuàng)建一個(gè)閉包, 閉包產(chǎn)生了對局部變量$counter的引用.
 *      3. 函數(shù)counter返回創(chuàng)建的閉包, 并銷毀局部變量, 但此時(shí)有閉包對$counter的引用, 
 *          它并不會被回收, 因此, 我們可以這樣理解, 被函數(shù)counter返回的閉包, 攜帶了一個(gè)游離態(tài)的
 *          變量.
 *      4. 由于每次調(diào)用counter都會創(chuàng)建獨(dú)立的$counter和閉包, 因此返回的閉包相互之間是獨(dú)立的.
 *      5. 執(zhí)行被返回的閉包, 對其攜帶的游離態(tài)變量自增并返回, 得到的就是一個(gè)計(jì)數(shù)器.
 * 結(jié)論: 此函數(shù)可以用來生成相互獨(dú)立的計(jì)數(shù)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
// 一個(gè)基本的購物車，包括一些已經(jīng)添加的商品和每種商品的數(shù)量。
// 其中有一個(gè)方法用來計(jì)算購物車中所有商品的總價(jià)格。該方法使用了一個(gè)closure作為回調(diào)函數(shù)。
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);
            };
        //使用用戶自定義函數(shù)對數(shù)組中的每個(gè)元素做回調(diào)處理
        array_walk($this->products, $callback);
        return round($total, 2);;
    }
}
$my_cart = new Cart;
// 往購物車?yán)锾砑訔l目
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);
// 打出出總價(jià)格，其中有 5% 的銷售稅.
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)