Posted by Jochem Maas on 10/24/05 22:53

nicely put.

Oliver Grätz wrote:
> GamblerZG schrieb:
>
>>>But what benefit is there is having it as an explicitly "abstract"
>>>class? Why can't it just be a "normal" class definition which you
>>>inherit from?
>>
>>The idea is that a high-level language should prohobit you from doing
>>things that do not make sence. Why they implemented it in PHP? Because
>>it's there in Java, I guess.
>
>
> No, it's there because it makes sense.
> If you derive from an abstract class the mechanism forces you to
> implement the abstract methods. Think of this:
>
> class Super
> {
> public function check() {} //no code!
> public function huba()
> {
> /* code */
> $this->check(); // use of method
> }
> }
> class MyClass extends Super {}
>
> This is what you do without having abstract classes. You put an empty
> method into the class. You rely on remembering that test() has to be
> filled with meaning in the subclass. You are even allowed to forget
> implementing check() which might get you into trouble because the
> check() is what you meant to be called for ensuring the data integrity
> of the data you intend to use a few lines later.
>
> Or worse: You leave out the method in the superclasse and only state in
> the documentation that there has to be a check() method in subclasses.
> This is the way to forgetting to implement all kinds of stuff.
>
> So there is this mechanism called "abstract class":
>
> abstract class Super
> {
> abstract public function check();
> public function huba()
> {
> /* code */
> $this->check(); // use of method
> }
> }
> class MyClass extends Super {}
>
> Now, you enforce several things:
> - Super cannot be instantiated.
> It is not complete and PHP knows about this.
> - MyClass is not complete until you implement a check().
> This way you have to actively say "I don't need a check."
> by putting an empty check() into MyClass.
>
> Even better: You can decide to implement just some of the abstract
> methods of Super. Then PHP forces you to declare your subclass as
> abstract, too. This allows for partially complete class trees and it is
> not up to you to remember which classes are ready to use and which are not.
>
> No, abstract classes are not just there "because Java has them", they
> exits because they help you in managing your code repository and because
> they prohibit you from doing stupid things with the code.
>
> OLLi
>

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