Some usage examples of php anonymous functions

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Release: 2023-03-11 18:08:02
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Anonymous functions (Anonymous functions), also called closure functions, allow temporarily creating a function without a specified name. The value most often used as the callback function (callback) parameter. Of course, there are other applications as well.

Example #1 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. A semicolon must be added at the end:

Example #2 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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closure Packages can inherit variables from the parent scope. Any such variables should be passed in using the use language construct.

Example #3 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 declared at the head of the function or class. 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). Examples are as follows:

Example #4 Closures and Scope

<?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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Anonymous functions are currently implemented through the Closure class.


Version Description


5.4.0 $this can be used for anonymous functions.

5.3.0 Anonymous functions can be used.


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