What is php delayed static binding? Detailed explanation of delayed static binding example code

php delayed static binding: refers to the self of the class, which is not based on the time of definition, but based on the running results during calculation.

(1) When the subclass instantiated object $stu calls the say method, it runs in the parent class Human, so self::hei() in say() is the hei() of the parent class. )method.

(2) static::method name(): If you use the static keyword, you will first search for the method in the subclass; if not found, search it in the parent class.

Usage scenarios

First observe the following code:

##

abstract class base {
  //do sth
}
class aClass extends base{
  public static function create(){
    return new aClass();
  } 
}
class bClass extends base{
  public static function create(){
    return new bClass();
  }
}
var_dump(aClass::create());
var_dump(bClass::create());

Output:

object(aClass)#1 (0) { } object(bClass)#1 (0) { }

The above aClass and bClass inherit from the abstract class base, but the static method create() is also implemented in the two subclasses. Following the oop idea, this repetitive code should be implemented in the parent class base.

Improved code

abstract class base {
  public static function create(){
    return new self();
  } 
}
class aClass extends base{
}
class bClass extends base{
}
var_dump(aClass::create());
var_dump(bClass::create());

The current code seems to be in line with our previous ideas, and the create() method is shared in the parent class. So let's run it and see what happens.

Cannot instantiate abstract class base in...

Unfortunately, the code does not seem to run as we expected. self() in the parent class is parsed as base This parent class does not inherit from its subclasses. So in order to solve this problem, the concept of delayed static binding was introduced in php5.3.

Delayed static binding

abstract class base {
  public static function create(){
    return new static();
  } 
}
class aClass extends base{
}
class bClass extends base{
}
var_dump(aClass::create());
var_dump(bClass::create());

This code is almost the same as the previous one. The difference is that self is replaced with the static keyword, and static will be parsed As a subclass instead of a parent class, this can solve the problems encountered above. This is PHP's delayed static binding.

Finally, run the code and get the final desired result.

object(aClass)#1 (0) { } object(bClass)#1 (0) { }

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