Detailed usage methods in PHP closure function() use()

PHP’s closure (Closure) is also anonymous function. It was introduced in PHP5.3.

The syntax of closure is very simple. The only keyword that needs attention is use. Use means to connect the closure with external variables.

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

Several functions of closure:

1 Reduce the code of foreach loop

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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(&#39;butter&#39;, 1);  
$my_cart->add(&#39;milk&#39;, 3);  
$my_cart->add(&#39;eggs&#39;, 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  
?>

If we transform the getTotal function here, we must use foreach

2 Reduce function parameters

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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";};  
}

If we use the usual method, we will put the inner into the html function parameters , so that whether it is code reading or use It’s better to use closure

3 Unlock 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(&#39;error&#39;);};//rewrite $fib variable   
   echo $lie(5);// error   because $fib is referenced by closure

Note that use in the above question uses &, if you don’t use & here, an error will occur n-1) Yes The function cannot be found (the type of fib was not defined before)

So when you want to use a closure to cancel the loop function, you need to use the form

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

4 About Delayed binding

If you need to delay binding the variables in use, you need to use references, otherwise a copy will be made and placed in use when defined

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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)

Use references And not using references means assignment when calling or assigning when declaring

The above is the detailed usage method of PHP closure function() use() that I compiled for everyone. I hope it will be helpful to everyone in the future. help.

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