callback function in php

* 2. 2 functions that execute callbacks

* Tip: What is a callback?

* The functions we call provided by the PHP system are called direct calls, also called: direct calls

* When the PHP system calls a user-defined function, it must be called through a proxy function, which is called an indirect call, also called a callback

* This is what we learned today about call_user_func() and call_user_func_array() The proxy function

* can call our custom function instead of the system

* 1.call_user_func_array($callback, $array): Use the array parameters to execute the callback function

* 2.call_user_func($callback, $array): The first parameter is used as the callback function call

* Note: 1. Usually there is no need to write parameters in the callback, but to obtain them through other functions; 2. Parameters Passing by reference is not allowed

//1. Parameters are passed in one by one using: call_user_func()

//Single parameter

echo call_user_func(function(){
    //如果匿名回调没写参数,可以通过func_get_args()获取
    return '欢迎来到'.func_get_arg(0);
},'php中文网');
echo '<hr>';
echo call_user_func(function($site){
    return '欢迎来到'.$site;
},'php中文网');
echo '<hr>';

//Multiple parameters, actual parameter amount The number of callback parameters must be consistent, and any excess will be ignored

echo call_user_func(function($site,$course){
    return '欢迎来到'.$site.'学习'.$course.'课程';
},'php中文网','php');
echo '<hr>';
//支持调用类中的方法做为回调
class Demo1
{
    //普通方法
    public function sum($a, $b)
    {
        return $a+$b;
    }
}
class Demo2
{
    //静态方法
    public static function multi($a,$b)
    {
        return $a*$b;
    }
}

//Call a normal method: the callback must be passed in as an array: [object, 'method name']

$obj = new Demo1;
echo call_user_func([$obj,'sum'],10,15);

//php5 .4 or above, can be abbreviated:

echo call_user_func([(new Demo1()),'sum'],10,15);
echo '<hr>';

//Call static method: there are two ways: string and array

//String: 'Class name::Method name'

echo call_user_func('Demo2::multi',10,15);

//Array: [class name, 'method name']

echo '<hr>';
echo call_user_func(['Demo2','multi'],20,5);

//If there is a namespace, just add the namespace string before the class name, or use the constant __NAMESPACE__

//Understand call_user_func(), then call_user_func_array() is very simple, only the parameters are different

* 2.call_user_func_array(callback, array)

* Only accept Two parameters: callback, index array, the parameters passed to the callback are all packed into the index array

* The only difference from call_user_func(array,arg1...) is that the method of passing parameters is different

* Callbacks also support: string function names, class names, arrays, anonymous functions

echo '<hr>';
echo call_user_func_array(function(){
    //查看传递给回调的参数
//    return print_r(func_get_args(),true);
    
    $msg = '前端开发的基础知识包括:';
    //遍历参数数组
    foreach (func_get_args() as $value) {
        $msg .= $value.',';
    }
    //去掉未尾逗号,并替换成感叹号
    return rtrim($msg,',').'!';
    
}, ['html','css','javascript']);
echo '<hr>';
class Demo3
{
    public function func1()
    {
        return __METHOD__.'<pre>'.print_r(func_get_args(),true).'</pre>';
    }
}
class Demo4 
{
    public static function func2()
    {
        return __METHOD__.'<pre>'.print_r(func_get_args(),true).'</pre>';
    }
}

//Methods in callback classes

echo call_user_func_array([(new Demo3),'func1'], ['php','java','c']);

//Callbacks for calling static methods:

//1. Use array parameter method

echo call_user_func_array(['Demo4','func2'], ['html','css','jQuery']);

//2. Use string parameter method

echo call_user_func_array('Demo4::func2', ['html','css','jQuery']);

//If there is a namespace, you only need to add the namespace before the class name Or __NAMESPACE__ will do

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