PHP Class Method Inheritance

Question

I'm trying to override a class' parent function with some changes. I have one argument that needs to be type-hinted on the parent and on the child it's a class that extends that type-hint:

class BaseObject { 
  //...
}

class NewObject extends BaseObject {
  //...
}

// -----------------------------------

class ParentClass {
  function method(BaseObject $obj) {
     //...
  }
}

class ChildClass extends ParentClass {
  function method(NewObject $obj) {
     //...
  }
}

PHP is returning:

Declaration of ChildClass::method(NewObject $obj) should be compatible with ParentClass::method(BaseObject $obj)

I find this kind of odd, since NewObject is an instance of the BaseObject.

Do you have a question?

Peter
– Peter

2020-07-03 15:23:32 +00:00
Commented Jul 3, 2020 at 15:23 — Peter
– Peter, Commented Jul 3, 2020 at 15:23

Ary Wibowo · Accepted Answer · 2020-07-04 23:23:17Z

1

I think that you need is an interface. If both class implement same interface, you can do Dependency Injection on the method that you want.

interface InterfaceName {
  //...
}

class BaseObject implements InterfaceName { 
  //...
}

class NewObject extends BaseObject implements InterfaceName {
  //...
}

class ParentClass {
  function method(InterfaceName $obj) {
     //...
  }
}

class ChildClass extends ParentClass {
  function method(InterfaceName $obj) {
     //...
  }
}

Reference : https://www.php.net/manual/en/language.oop5.interfaces.php

answered Jul 4, 2020 at 23:23

Ary Wibowo

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1 Comment

Francisco Castel-Branco Over a year ago

Thank you! This is what I was looking for. I use interfaces a lot, but forgot to pass it as an argument type, somehow.

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