Description and usage of static in php

* Elaborate on static

* 1. Purpose:

* 1. Declare static members in the class

* 2. Declare static variables in the function

* 3. Late static binding

*

* 2. Features:

* 1. Static members belong to classes and must be accessed using classes

* 2. Static methods are special and allow object access, but not recommended

* 3. The range parsing operator must be used:: to access, and the object access operator -> access is not allowed

* 4. Static properties are only allowed to be initialized using literals (characters/numeric values/arrays) or constants (expressions/variables/objects are prohibited)

*

* 3. Later static binding Fixed/delayed static binding

* Note: The introduction on the php.net official website is very obscure, here is a simplified explanation

* 1. What is forwarding call?

* Answer: In human terms, static methods are executed in the form of callbacks. To use callbacks, you must specify the caller or proxy function.

* The caller can be self, parent, static

* There are many proxy functions:

* forward_static_call(callable,arg1...)

* forward_static_call_array(callable,array)

* call_user_func(callable,arg1...)

* call_user_func_array(callable,array)

class Demo1 
{
    public static function test1()
    {
        //返回参数:func_get_args(void )返回参数数组
        return implode(',', func_get_args());
    }
    
    //后期静态绑定(最后再创建这个父类方法用来教学)
    public static function test3()
    {
        //调用当前类的静态方法
//        return self::test1('php','mysql','thinkphp');
        //使用static,动态判断是哪个类在调用test1()方法
        //类方法的调用者,在声明时指定,是前期调用,在编译阶段完成
        //类方法的调用者,在执行时指定,是后期调用,在运行阶段完成
        return static::test1('php','mysql','thinkphp');
        
    }
}
class Demo2 extends Demo1 
{
    //重写父类静态方法
    public static function test1()
    {
        return __METHOD__;
    }
    
    public static function test2()
    {
        //1.传统调用父类静态方法
        return parent::test1('php中文网');
        
        //2.用代理函数调用父类静态方法
        //return forward_static_call(['Demo1','test1'],'Hello','PHP中文网');
        
        //下call_user_func()功能完全一样
        //return call_user_func(['Demo1','test1'],'Hello','PHP中文网');
        
        //调用本类的静态方法
        //return forward_static_call(['Demo2','test1']);
        
        //如果第一个参数是一个字符串,是指一个全局函数,不属于任何类
        //return forward_static_call('test3','www.php.cn');
    }
    
    
}
//创建一个外部函数
function test3()
{
    return '我是类外部定义的一个函数,'. func_get_arg(0);
}
//echo Demo2::test2();
//后期静态绑定
//用Demo2类静态调用test3(),而test3()中调用了本类的test1()
echo Demo2::test3();
/**
 * 分析
 * 1. test3()方法在Demo1类中
 * 2. Demo2类继承自Demo1,所以可以用Demo2访问test3()
 * 3. test3()中访问了当前类的test1()方法,当然是Demo1类的test1()
 * 4. 但是我是用Demo2类调用的test3(),因此我的本意,肯定是想调用Demo2中重载的test1()
 * 5. 那么,如果能让当前静态方法的调用者,根据继承关系的上下文自动进行判断呢?
 * 6. 在静态方法前使用static关键字,这样就可以自动判断是哪个类在调用我了~~
 * 7. 运行时会自动将static,替换成Demo2类
 */
echo &#39;<hr>&#39;;
//思考:在Demo1中调用test3()会输出什么结果?
echo Demo1::test3();

* 1. The Demo1 class will be output The running result of the test1() method in

* 2. Because the current caller is Demo1, static will be automatically replaced with Demo1

during runtime.

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