PHP implements late static binding

The working principle of late static binding is to store the class name in the previous "non-forwarding call" (non-forwarding call). When making a static method call, the class name is the one explicitly specified (usually on the left side of the :: operator); when making a non-static method call, it is the class to which the object belongs.

The so-called "forwarding call" (forwarding call) refers to static calls made in the following ways: self::, parent::, static:: and forward_static_call(). You can use the get_called_class() function to get the class name of the called method, and static:: points out its scope.

limitations of self::

Use self:: or __CLASS__ for a static reference to the current class, depending Define the class in which the current method is located:

Example:

class  A  {
    public static function  who () {
        echo  __CLASS__ ;
    }    public static function  test () {
         self :: who ();
    }
}class  B  extends  A  {
    public static function  who () {
        echo  __CLASS__ ;
    }
}

B :: test ();

Result:

A

static (late static binding)

Late static binding was intended to circumvent the limitation by introducing a new keyword representing the class that was initially called by the runtime. Simply put, this keyword allows you to refer to class B instead of A when calling test() in the above example. It was finally decided not to introduce new keywords, but to use the already reserved static keywords.

Example:

<?phpclass A {
    public static function who() {
        echo __CLASS__;
    }    public static function test() {
        static::who(); // 后期静态绑定从这里开始
    }
}class B extends A {
    public static function who() {
        echo __CLASS__;
    }
}

B::test();?>

Result:

B

The difference between static and $this

In a non-static environment, what is called The class of is the class to which the object instance belongs. Since $this-> will try to call the private method in the same scope, static:: may give different results. Another difference is that static properties can only be called with static::.

Example: Calling a private method

<?phpclass A {
    private function foo() {
        echo "success!\n";
    }    public function test() {
        $this->foo();        static::foo();
    }
}class B extends A {
   /* foo() will be copied to B, hence its scope will still be A and
    * the call be successful */}class C extends A {
    private function foo() {
        /* original method is replaced; the scope of the new one is C */
    }
}$b = new B();$b->test();$c = new C();$c->test();   //fails

Result:

success!
success!
success!
Fatal error:  Call to private method C::foo() from context 'A' in /tmp/test.php on line 9

Forwarded and non-forwarded calls

Analysis of late static binding Will continue until a fully parsed static call information is obtained. On the other hand, if the static call is made using parent:: or self:: the call information will be forwarded.

Example:

class A {
    public static function foo() {
        static::who();
    }    public static function who() {
        echo __CLASS__."\n";
    }
}class B extends A {
    public static function test() {
        A::foo();        parent::foo();        self::foo();
    }    public static function who() {
        echo __CLASS__."\n";
    }
}class C extends B {
    public static function who() {
        echo __CLASS__."\n";
    }
}

C::test();

Result:

ACC

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