Alex Rivera | Logout

when using self, parent, static and how?

Asked 2012-05-08T18:14:46.020
18

If by now I understood a little in ststic Now I realize I do not understand anything. I'm so confused and I struggle to understand and I can not. Someone can explain this program when using self, parent, static and how All the smallest change I do changes the result without that I can not understand what's going on. thanks a lot ..

the code from http://docs.php.net/language.oop5.late-static-bindings

<?php
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();
?>

The out put are:

A
C
C
php oop static
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2 Answers

10

Look at http://php.net/manual/en/language.oop5.static.php. It says:

Declaring class properties or methods as static makes them accessible without needing an instantiation of the class.

...

Because static methods are callable without an instance of the object created, the pseudo-variable $this is not available inside the method declared as static.

You cannot use $this because when calling a static method, there is no instantiated class object to be placed in the $this variable. So you use self::.

parent:: is referring to the parent class that the current class is extending. For example, for Class C the parent class is Class B, and for Class B, the parent class is Class A. See http://php.net/manual/en/keyword.parent.php.

You use static methods when you want the function to be accessible without actually having an instance of that class declared.

Upon closer inspection of your question, your link points to Late Static Bindings. The first two examples in that page pretty clearly indicate the need for the static:: syntax, but to clarify for the example you posted:

Take a look at the foo() method in Class A. It calls static::who(). This means that the method who() will be called in the scope of the class that called the function, instead of the scope of the class where the function is defined. So if you were to call C::foo(), it would echo C.

If, instead, it called self::who(), it would be calling A::who(). Because within Class A, self:: refers to A.

Hopefully that helps.

answered 2012-05-08T18:25:35.430
6

The key to the answer is static::who(), remember static:: means you call the method with the actual class (in our case - C).

so C::test() run as follows:

A::foo();   -> calls to A::foo() therefor echo A
parent::foo(); -> calls to C parent (which is B), B::foo() inherits A::foo() which calls to static::who(), but our actual class is C, therefor echo C
self::foo(); -> again calls to foo() which calls to static::who() with our actual class C

if instead of static::who() foo was calling self::who() you would have get three A as a result.

answered 2012-05-08T18:53:35.123

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