What is the difference between self and static in php

The difference between self and static in php: self can only refer to methods in the current class (current class), while static allows function calls to bind methods in the calling class (calling class) at runtime.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

The difference between self and static in php

Through some examples, we can easily see the difference between self and static. Suppose we have class Car - it has two methods, model and getModel. Note that here we use the keyword self.

class Car
{
    public static function model()
    {
         self::getModel();
    }

    protected static function getModel()
    {
        echo "I am a Car!";
    }

}

Call static method

Car::model();

Get output

I am a Car!

The keyword self causes us to call the getModel method of class Car and output the text "I am a Car!".

Next we add a new class, class Mercedes, which inherits from class Car. The code is as follows:

class Mercedes extends Car{

    protected static function getModel()
    {
        echo "I am a Mercedes!";
    }

}

When we call Mercedes::model(), guess what the result is?
Maybe you think the result will be:

I am a Mercedes!

But the actual output is:

I am a Car!

Why is this?

Explanation of self

The working principle of the keyword "self" is: it will call the method of current class (current class). Because the model method is only defined in class Car, the current class is class Car for it. Self::getModel() in the model naturally calls the getModel method in class Car.

This behavior does not seem to be what we want, and it does not comply with object-oriented design principles. How to solve it? You can use the keyword static.

static keyword and delayed static binding (late static binding)

In PHP5.3, a new feature has been added called delayed static binding. It can help us achieve polymorphism and solve the above problems. In simple terms, delayed static binding means that when we call an inherited method with the static keyword, it will be bound to the calling class at runtime. In the above example, if we use delayed static binding (static), it means that when we call "Mercedes::model();", the getModel method in class Mercedes will be called. Because Mercedes is our calling class. Example of delayed binding

class Car{
    public static function model()
    {
         static::getModel();
    }    protected static function getModel()
    {
        echo "I am a Car!";
    }

}

We just replaced self in class Car with static and did not modify class Mercedes.

Now we call

Mercedes::model();

to get the output

I am a Mercedes!

Versions below php 5.3 cannot use delayed static binding

Note that versions before php 5.3 cannot Use delayed static binding. If you try to run the above example on a version below PHP 5.3, an error will be reported.

self and static in php

Now we replace self in the example with static. You can see that the difference between the two is: self refers to the current class (current class) method, while static allows function calls to bind methods in the calling class at runtime.

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