Briefly talk about php delayed static binding

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 in two subclasses At the same time, the static method create() is implemented. Following the oop idea, this kind of repeated 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. The create() method is shared in the parent class. 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. static will be resolved to 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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