How to implement callbacks in PHP?

In PHP, a callback is a function object/reference of a callable type; callback (or callable) variables can be used as functions, object methods and static class methods. There are many ways to implement callbacks. This article will introduce some of them. I hope they will be helpful to everyone. [Video tutorial recommendation: PHP tutorial]

1. Standard callback

Example: use call_user_func( ) function calls a function whose argument is the function name.

<?php 
header("content-type:text/html;charset=utf-8");
function text1(){
    echo &#39;这个是text1<br>&#39;;
};
call_user_func(&#39;text1&#39;);
  
?>

Output:

这个是text1

Explanation: A call_user_func() function is called, and then the call_user_func() function calls back the text1() function during execution.

2. Static class method callback

Example: Use the call_user_func() function to call a static class method, where the parameter is a parameter containing the class name and the method to be called. array.

<?php 
header("content-type:text/html;charset=utf-8");
class Demo { 
  
    // 用于输出字符串的函数
    static function someFunction() { 
        echo "父级函数输出 <br>"; 
    } 
} 
  
class Article extends Demo { 
  
    // 用于输出字符串的函数 
    static function someFunction() { 
        echo "子级函数输出 <br>"; 
    }    
} 
  
// 静态类方法回调
call_user_func(array(&#39;Article&#39;, &#39;someFunction&#39;)); 
  
call_user_func(&#39;Article::someFunction&#39;); 
  
// 相对静态类方法回调
call_user_func(array(&#39;Article&#39;, &#39;parent::someFunction&#39;)); 
  
?>

Output:

子级函数输出
子级函数输出
父级函数输出

3. Object method callback

Example: Use the call_user_func() function to call the object method, where the parameters include object variables and an array of string names of methods to be called.

<?php 
header("content-type:text/html;charset=utf-8");
class Demo { 
  
    // 输出字符串的函数
    static function someFunction() { 
        echo "PHP中文网 <br>"; 
    } 
  
    // 输出字符串的函数
    public function __invoke() { 
        echo "__invoke()函数<br>"; 
    } 
} 
  
// 类对象
$obj = new Demo(); 
  
// 对象方法调用
call_user_func(array($obj, &#39;someFunction&#39;)); 
  
call_user_func($obj); 
  
?>

Output:

PHP中文网 
__invoke()函数

4. Closure callback

Example: Use the array_map() function to assign valid values ​​to the closure function Array of arguments makes a closure function callable by making a standard call or by mapping a closure function, where arguments is an array of the closure function and its valid arguments.

<?php 
header("content-type:text/html;charset=utf-8");
// 用于输出<br>
$print_function = function($string) { 
    echo $string."<br>"; 
}; 
  
// 字符串数组 
$string_array = array("PHP", "Python", "MySQL"); 
  
// 可调用闭包
array_map($print_function, $string_array);
?>

Output:

PHP
Python
MySQL

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