Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:114243
MIME-Version: 1.0
References: <V7C5-r6tzKmxjhPnvy9gtfdMtxkj0z_PJphaehaqcPsOLX0pEKtGU4A8EuSKyS-cbZl5HPVA2ejXCuXXOfOksH9VACGOKT3awRsr9aSNIg8=@protonmail.com>
 <CAC5V6gjW4hhEx=m6RuFoR+D5QCiNbHWyAH5Wd6-nwbH7noxFmg@mail.gmail.com>
 <AM6PR01MB53369F48110B79A241E74C6ABB409@AM6PR01MB5336.eurprd01.prod.exchangelabs.com>
 <CAC5V6giZ-LaSbg0-eQZoqPxDBonsSbococNLNg8YAsgs8o6R2Q@mail.gmail.com> <AM6PR01MB533616F6DB44AB813579FDC6BB409@AM6PR01MB5336.eurprd01.prod.exchangelabs.com>
In-Reply-To: <AM6PR01MB533616F6DB44AB813579FDC6BB409@AM6PR01MB5336.eurprd01.prod.exchangelabs.com>
Date: Wed, 28 Apr 2021 18:47:41 +0200
Message-ID: <CAC5V6gg=JuzAUQN0QoiQGN=Qi3zkJ1PQbNRLKe1DsU06Oq4JxQ@mail.gmail.com>
To: Tony Marston <tonymarston@hotmail.com>
Cc: PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000b3f1eb05c10b2341"
Subject: Re: [PHP-DEV] [RFC][Draft] Sealed Classes
From: guilliam.xavier@gmail.com (Guilliam Xavier)

--000000000000b3f1eb05c10b2341
Content-Type: text/plain; charset="UTF-8"

Re-forwarding to the list (please stop replying to me in private, thanks).
Also re-answering but I will stop there because that's too much digression
for a partial quote of my initial message.

On Wed, Apr 28, 2021 at 5:30 PM Tony Marston <tonymarston@hotmail.com>
wrote:

> On 28/04/2021 14:30, Guilliam Xavier wrote:
> > Forwarding to the list, and answering:
> >
> > On Wed, Apr 28, 2021 at 9:51 AM Tony Marston <tonymarston@hotmail.com>
> > wrote:
> >
> >> On 27/04/2021 17:22, Guilliam Xavier wrote:
> >>> On Sat, Apr 24, 2021 at 12:55 PM Saif Eddin Gmati <
> azjezz@protonmail.com
> >>>
> >>> wrote:
> >>>
> >>>
> >>> To me the first sentence of the RFC is debatable:
> >>>
> >>>> The purpose of inheritance is code reuse, for when you have a class
> that
> >>>> shares common functionality, and you want others to be able to extend
> it
> >>>> and make use of this functionality in their own class.
> >>>
> >>> That sounds like [abstract] base classes, which certainly permit that,
> >> but
> >>> I wouldn't state that "the purpose" of [designing] class hierarchies is
> >>> "code reuse", which can also (better?) be achieved with traits or even
> >>> simply composition
> >>
> >> I completely disagree that the first sentence of that RFC is debatable
> >> as I consider it to be totally accurate. When you use inheritance via
> >> the 'extends' keyword then every method in the superclass is shared by
> >> the subclass. In the subclass you have the option to override the
> >> implementation of any method in the superclass, or you can add new
> >> methods of your own.
> >
> >
> > But does that necessarily mean that "The purpose of inheritance is code
> > reuse"?
>
> Can you show me any description of OOP which says that the purpose of
> inheritance is anything other than code reuse?


I suspect it won't convince you but you can find quotes like: "The point of
inheritance is to take advantage of polymorphic behavior NOT to reuse code,
and people miss that, they see inheritance as a cheap way to add behavior
to a class." (not that I endorse it absolutely, but that's an example of
different opinion).

What other purose could
> it possibly serve?
>

Modeling a problem domain? Enforcing a contract?


> > This superclass may be abstract, but it need not
> >> be. The methods it contains may be abstract, but they need not be.
> >>
> >
> > I didn't say that they need (the brackets meant "optionally"). And does
> it
> > really matter actually?
>
> Yes. If you inherit any abstract methods you are not actually inheriting
> anything. Not only do you have to manually define in the subclass any
> method which is defined as abstract, you also have to provide the
> implementation.
>

My bad, I should have inserted the reply one sentence earlier: I was
referring to "[abstract] base classes" (from my original quote), not
abstract methods. Of course if the goal is to share implementation there
must be concrete methods in the base class...


> >> According to the Gang of Four the way to avoid the problems caused by
> >> the overuse of inheritance is to only inherit from an abstract class,
> >> which is precise what I do. I am famous for having an abstract table
> >> class in my framework which contains hundreds of methods and thousands
> >> of lines of code, and because each of my 400 concrete table classes
> >> inherits from the same abstract table class that is a LOT of code which
> >> is shared. This abstract table class also allows me to use the Template
> >> Method Pattern (which is mentioned in the Gang of Four book) so that all
> >> the invariant methods are defined in the abstract class which means that
> >> each subclass need only contain the variable "hook" methods for which it
> >> needs to provide an implementation.
> >>
> >
> > Well, PHP is flexible. I have seen many combinations of (one or several
> of)
> > interface, [abstract] class, trait, composition... depending on the
> context.
>
> The fact that there are now several ways of reusing code does not
> detract from the original statement that "The purpose of inheritance is
> code reuse".
>

See above, plus a quick web search for things like "inheritance misuse" or
"class SplStack extends SplDoublyLinkedList" I think shows it's a
controversial subject (hence "debatable" at least).


> >> When you say that code reuse can be better achieved with traits or
> >> object composition I have to disagree.
> >
> >
> > I said "also (better?)", not just "better". But one can think "no" to
> > "better?" ;)
> >
>  >
> > Object composition is used only
> >> by those idiots who overuse inheritance,
>
> In the GoF book on design patterns, which was first published in 1995,
> it quite clearly stated that any problems emanating from inheritance
> were causes by its overuse, and that a solution would be to only ever
> inherit from abstract classes.


"class Stack extends AbstractList" is still wrong.

If people are still overusing inheritance
> 25 years later and ignoring the advice given by the Gang of Four then I
> feel justified in calling them idiots.
>

:/


> > and there is no evidence that
> >> traits are "better" than inheritance.
> >
>  >> By the way, is there evidence to the contrary? (genuine question)
>
> Until somebody does a comparison of all the different ways in which code
> can be shared there can never be a definitive answer.
>

Agreed.


> >> Inheritance, when used sensibly, is still the best way to share code.
> >>
> >
> > Your opinion, maybe not unanimity (nor absolute truth).
>
> The GOF book says so, and it also says that the Template Method Pattern
> - which can only be used through inheritance - is a fundamental
> technique for code reuse.


Are The GoF Book opinions (still) unanimity? Also, did PHP traits exist in
1994? (rhetorical questions) (and BTW, I know, composition did already
exist, but not the point)

In my humble opinion any method of code reuse
> which does not allow the Template Method Pattern is automatically inferior.
>

You said it: "in [your] humble opinion" :) I have mine too. Anyone can
(obviously).

More importantly, even if I were to agree that "inheritance" be the best
method of "code reuse" (and I have to admit it is widely used like that), I
still wouldn't state that that's "the [absolute and only] purpose" of it.


> Regards,
>
> Tony Marston
>

Regards,

-- 
Guilliam Xavier

--000000000000b3f1eb05c10b2341--