New self vs. new static?

Question

I am converting a PHP 5.3 library to work on PHP 5.2. The main thing standing in my way is the use of late static binding like `return new static($options);` , if I convert this to `return new self($options)` will I get the same results? What is the difference between `new self` and `new static`?

Answer 1

If you convert return new static($options) to return new self($options), you may not get the same results as there is a difference between new self and new static.

When using new self, the object will always be an instance of the class where it was defined, regardless of any inheritance that takes place. On the other hand, when using new static, the object will be an instance of the class where it is called, which can be useful for inheritance purposes.

Here's an example to illustrate the difference:

Copy Code

class ParentClass {

public function createSelf() {

return new self();

}

public function createStatic() {

return new static();

}

}

class ChildClass extends ParentClass {}

$obj = new ChildClass();

$selfObj = $obj->createSelf(); // Returns an instance of ParentClass

$staticObj = $obj->createStatic(); // Returns an instance of ChildClass

In the above example, createSelf() method returns an instance of ParentClass because self refers to the class where it is defined, which is ParentClass. However, the createStatic() method returns an instance of ChildClass because static refers to the class where it is called, which in this case is ChildClass.

So, if you change return new static($options) to return new self($options), you may end up with an object that is not correctly inheriting properties or methods from child classes, since self always refers to the class where it is defined, whereas static refers to the class where it is called.