PHP's Closure (Closure) is also an anonymous function. was introduced by PHP5.3.

PHP's Closure (Closure) is also an anonymous function. was introduced by PHP5.3.

The syntax of a closure is simple, and the key word to be aware of is that only use,use means connecting closures and external variables.

123	$a= function() use($b) {}

Several functions of closures: 1 reducing the Loop code for foreach

such as the example cart in the handbook http://php.net/manual/en/functions.anonymous.php

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<?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);            };                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?>

Here, if we transform the Gettotal function, we must use the foreach

2 Reducing the parameters of a function

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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";};}如果是使用平时的方法，我们会把inner放到html函数参数中，这样不管是代码阅读还是使用都不如使用闭包

3 Lifting the recursive function

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<?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

Note that the use of the &amp in the above title is not used & error will occurFIb(

n-1) is unable to find function (the type of FIB is not previously defined)

So when you want to use closures to remove the loop function, you need to use the

1234	<?php$recursive= function () use(&$recursive){// The function is now available as $recursive}

Such a form

4 About delay binding

If you need to delay the binding of a variable inside a use, you need a reference, or you will make a copy of it when you define it.

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<?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)

The use of references and non-use of references represents the assignment of a call, or the assignment of a value at the time of declaration

PHP's Closure (Closure) is also an anonymous function. was introduced by PHP5.3.