What is an anonymous function-PHP Tutorial-php.cn

What is an anonymous function

藏色散人

Release： 2023-04-04 20:10:01

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Anonymous functions

Anonymous functions (Anonymous functions), also called closures, allow you to temporarily create a function without a specified name. The value most commonly used as a callback function argument. Of course, there are other applications as well.

What is an anonymous function

Anonymous functions are currently implemented through the Closure class.

Anonymous function example

<?php
echo preg_replace_callback(&#39;~-([a-z])~&#39;, function ($match) {
    return strtoupper($match[1]);
}, &#39;hello-world&#39;);
// 输出 helloWorld
?>

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Closure functions can also be used as the value of variables. PHP will automatically convert this expression into an object instance of the built-in class Closure. The method of assigning a closure object to a variable is the same as the syntax of ordinary variable assignment, and a semicolon must be added at the end:

Example of anonymous function variable assignment

<?php
$greet = function($name)
{
    printf("Hello %s\r\n", $name);
};

$greet(&#39;World&#39;);
$greet(&#39;PHP&#39;);
?>

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Closures can inherit variables from the parent scope. Any such variables should be passed in using the use language construct. Starting from PHP 7.1, such variables cannot be passed in: superglobals, $this or have the same name as parameters.

Inherit variables from the parent scope

<?php
$message = &#39;hello&#39;;

// 没有 "use"
$example = function () {
    var_dump($message);
};
echo $example();

// 继承 $message
$example = function () use ($message) {
    var_dump($message);
};
echo $example();

// Inherited variable&#39;s value is from when the function
// is defined, not when called
$message = &#39;world&#39;;
echo $example();

// Reset message
$message = &#39;hello&#39;;

// Inherit by-reference
$example = function () use (&$message) {
    var_dump($message);
};
echo $example();

// The changed value in the parent scope
// is reflected inside the function call
$message = &#39;world&#39;;
echo $example();

// Closures can also accept regular arguments
$example = function ($arg) use ($message) {
    var_dump($arg . &#39; &#39; . $message);
};
$example("hello");
?>

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The output of the above routine is similar to:

Notice: Undefined variable: message in /example.php on line 6
NULL
string(5) "hello"
string(5) "hello"
string(5) "hello"
string(5) "world"
string(11) "hello world"

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These variables must be at the head of the function or class Ministry statement. Inheriting variables from the parent scope is different from using global variables. Global variables exist in a global scope, no matter which function is currently executing. The parent scope of a closure is the function that defines the closure (not necessarily the function that calls it).

Closures and scope examples:

<?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";
// 最后结果是 54.29
?>

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This article is an introduction to anonymous functions. I hope it will be helpful to friends in need!

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