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What is/is not considered to be good OO programming

Several months ago I started a thread with the title "What is/is not
considered to be good OO programming" which started a long and
interesting discussion.

I have condensed the arguments into a single article which can be
viewed at
http://www.tonymarston.net/php-mysql/good-bad-oop.html

I fully expect this to be the start of another flame war, so sharpen
your knives and get stuck in!

Tony (you do it your way and I'll do it better) Marston
http://www.tonymarston.net/
Jul 17 '05
52 6386
Matty wrote:

Wow, it's come back to life again!

Asbestos manufacturers everywhere must be looking forwards
to this one!

;p

Matt


FWIW, I still think it's better to have 12 different instances,
rather than 12 different classes <duck />... Not read it all yet,
just a quick search! I'll have a good read through tomorrow, but
I do think there aren't sufficient differences between tables in a
database to justify having a separate class to handle each table,
when a separate instance of a suitably generic class would handle it
OK.

I am definitely a TMTOWTDI kind of person, though, and I do agree
that fundamentally, if the software works, then it's good.

Matt
Jul 17 '05 #11
>> "Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
news:75******** *************** ***@posting.goo gle.com...


<snip>

http://www.tonymarston.net/php-mysql...tml#2003-12-05


(Yet Another Follow Up...)

Can't help wondering what the object composition argument was, and how
on earth you could do it in a logical manner.

A table "has a" page of records?

A page of records "has a" table (what would it do if it didn't?)

Personally, yeah, I think composition isn't the way to do it...

/me thinks How about a table "has a" table perhaps???
;p

Matt
Jul 17 '05 #12
André Næss <an************ *********@ifi.u io.no> wrote in message news:<bq******* ***@maud.ifi.ui o.no>...
Tony Marston:
Object composition
was also the crux of my argument, i.e.: where you see only inheritance, I
see inheritance and composition. From this we can only deduce that you in
fact did not properly understand my argument.
You argument is irrelevant as it serves no useful purpose when
discussing a single abstract class.


I wasn't discussing a single abstract class. I was discussing a solution to
a problem. The single abstract class and proliferation of new classes is
*your* solution. I tried to argue that a different, and IMO better approach
was possible.


It may seem better in your opinion, but to my mind it is different
without any obvious benefits, so there is no point in changing.
You didn't bother to learn about object composition until
*now*, yet you disagreed with my idea of using it in your case.
Object composition is not listed among the principles of OOP, so I
ignored it. When I did read about it the first thing that I saw was
that it was considered as an alternative method of dealing with
complex hierarchies. As I do not have a complex hierarchy (just two
levels) there seems no point in investigating it any further.
In other
words, you had decided that your solution *is* the best even before you
started the discussion,
I never said it was the best, I merely said that it is simple and it
works. As a follower of the KISS principle this is VERY important. Why
waste time on a complex solution if a simple one works?
despite the fact that you did not know much about OO.

André Næss


It is true that I have not been taught any OO, but that means that I
have not been taught the wrong things. What I have read about OO tells
me that objects are not that much different to components, and as I
have been working with a component-based development language for the
last 10 years all I did was to take my component-based design and
convert it to object-based. Simple and effective.

The fact that I do not do OOP in the way that you do it is irrelevant.
I can achieve rapid results my way, so my way is good for me (and a
few others according to the emails I have received).

Tony Marston
http://www.tonymarston.net/
Jul 17 '05 #13
Tony Marston wrote:
"Philipp Lenssen" <in**@outer-court.com> wrote in message
news:<bq******* ******@ID-203055.news.uni-berlin.de>...
André Næss wrote:

I was thinking the same. I saw the article, looked for
"compositio n", couldn't find it, and went away.


Just for you I have added a section on object composition. I hope you
like it.

http://www.tonymarston.net/php-mysql...tml#2003-12-05


You should differentiate between "has a" and "is a". I believe I
recently posted this here and the idea is neither mine nor new.

Inheritance examples in books often go by the examples of employees.
And employee "is a type of" person. So it would not make sense to use
object composition. (Not if person and employee are intended to be the
same anyway.) Because an employee shares attributes of a person but
includes his own.

Now let's say I have a class "webpage". Now this "webpage" has a
complex module "binary_ima ge" which will render images. You would use
simple object composition by creating a new instance of "binary_ima ge"
within "webpage".

Why is it composited and not inherited?
Because the webpage "has a" binary image. However, it's wrong to say
binary_image "is a type of" webpage. 'Cause it's not.

This was just an example. Usually I don't use global instances of
objects either in a class. Usually they just go right into the
function. E.g. using the file-system object from within a class on a
Windows server. Or handling XML.

And object composition structures the code and can make it more
readable. It's often more natural. But whatever approach suits you.
Don't forget however that if you're working in a team you can't just
say "my approach is better 'cause I like it and everyone should code
the way they want", because code must be managed by others. You
wouldn't expect your code to be rewritting from scratch or highly
refactored if you were sick for a week and someone else had to go
through it. So you should write code in ways accepted and used in your
team, and to find the best solution you must argue beyond personal
taste. Sometimes, you may even need to compromise.
Jul 17 '05 #14
"Doug Hutcheson" <do************ *******@nrm.qld .gov.au> wrote in message news:<B%******* ***********@new s.optus.net.au> ...
"Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
news:75******** *************** ***@posting.goo gle.com...
"Philipp Lenssen" <in**@outer-court.com> wrote in message

news:<bq******* ******@ID-203055.news.uni-berlin.de>...
André Næss wrote:

> Tony Marston:
> >
> > I have condensed the arguments into a single article which can be
> > viewed at
> > http://www.tonymarston.net/php-mysql/good-bad-oop.html
> >
> I just think it's funny that you still don't understand object
> composition. In your article you write: "How do you share code in OO
> systems? Through inheritance.", not even mentioning object
> composition. Object composition was also the crux of my argument,
> i.e.: where you see only inheritance, I see inheritance and
> composition. From this we can only deduce that you in fact did not
> properly understand my argument. That doesn't make the discussion any
> easier.
>

I was thinking the same. I saw the article, looked for "compositio n",
couldn't find it, and went away.


Just for you I have added a section on object composition. I hope you like

it.

http://www.tonymarston.net/php-mysql...tml#2003-12-05

Kiss, kiss

Tony Marston
http://www.tonymarston.net/


Tony,
A trifle defensive <grin>, but wholly correct. As another 25+ programmer, I
can state without too much fear of contradiction that the customer pays me
to solve his problem, not to write code which meets the approval of the
paradigm police.
More power to you, you rabid radical you!
Cheers,
Doug Hutcheson


People tend to describe me more as revolting than rebelling. Is there
a difference? :)

Tony Marston
http://www.tonymarston.net/
Jul 17 '05 #15
Matty <ma*******@askm enoquestions.co .uk> wrote in message news:<cG******* *************@w ards.force9.net >...
Matty wrote:

Wow, it's come back to life again!

Asbestos manufacturers everywhere must be looking forwards
to this one!

;p

Matt
FWIW, I still think it's better to have 12 different instances,
rather than 12 different classes <duck />...


According to the principles of OO you are not supposed to instantiate
an abstract class then feed it the implementation details, you are
supposed to put the implementation details in a subclass. If I were to
use the keyword 'abstract' in the class definition (as PHP 5 will
allow) you will find it impossible to instantiate an abstract class
directly, in which case you MUST use a subclass.

So, if I have 12 database tables each with a totally different set of
implementation details, then (according to the above-mentioned
principle) I must create 12 subclasses. I am right and you are wrong,
so score 1-0 to me :)
Not read it all yet,
just a quick search! I'll have a good read through tomorrow, but
I do think there aren't sufficient differences between tables in a
database to justify having a separate class to handle each table,
when a separate instance of a suitably generic class would handle it
OK.

I am definitely a TMTOWTDI kind of person, though, and I do agree
that fundamentally, if the software works, then it's good.

Matt


If it works then it is not wrong. But if method A is easier to
implement than method B, then (all other things being equal) method A
is better.

Tony Marston
http://www.tonymarston.net/
Jul 17 '05 #16
Matty <ma*******@askm enoquestions.co .uk> wrote in message news:<YN******* *************@w ards.force9.net >...
"Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
news:75******** *************** ***@posting.goo gle.com...


<snip>

http://www.tonymarston.net/php-mysql...tml#2003-12-05


(Yet Another Follow Up...)

Can't help wondering what the object composition argument was, and how
on earth you could do it in a logical manner.

A table "has a" page of records?

A page of records "has a" table (what would it do if it didn't?)

Personally, yeah, I think composition isn't the way to do it...

/me thinks How about a table "has a" table perhaps???
;p

Matt


A table has 4 legs and a set of drawers. Now, if I were to drop the
drawers and spread the legs..... :)
Tony Marston
http://www.tonymarston.net/
Jul 17 '05 #17
Tony Marston wrote:

FWIW, I still think it's better to have 12 different instances,
rather than 12 different classes <duck />...
According to the principles of OO you are not supposed to instantiate
an abstract class then feed it the implementation details, you are
supposed to put the implementation details in a subclass. If I were to
use the keyword 'abstract' in the class definition (as PHP 5 will
allow) you will find it impossible to instantiate an abstract class
directly, in which case you MUST use a subclass.


Depends on what you're doing with the "Table" class - if it's just a
question of iterating through the records, then one generic table class
would cover the vast majority of applications, without subclassing.

$parts = new Table ('partslist', 'partid', array('partid'= >'Part ID number',
'pdesc'=>'Descr iption', 'stockcount'=>' Number in stock'));

$customers = new Table ('customers', 'custid', arrya('custid'= >'Customer #',
'tel'=>'Contact Phone', 'sic'=>'SIC Industry Code'));

should work fine.

The other comment I'd make on this, is that "abstract" != "abstractio n".

Just because describing a table as

tablename
primarykey
fieldlist

is an abstraction, doesn't mean you need an abstract class for this - a "concrete"
class is fine for this model.

Personally, if I were writing a DB class lib, I'd have something along the lines of

Dataset
Table is-a Dataset
Query is-a Table, has-a SQL query

etc, etc
with Dataset being abstract, but that's just my take on it.

So, if I have 12 database tables each with a totally different set of
implementation details, then (according to the above-mentioned
principle) I must create 12 subclasses. I am right and you are wrong,
so score 1-0 to me :)
Yes and no, I would say. Yes, 12 tables requiring totally different handling
code would require 12 different classes. But the original tutorial, as I
remember it, showed 12 analogous tables (treated as a list of fields, etc)
that could all be handled by the same class as different instances, easily.

1-1 perhaps ;p

If it works then it is not wrong. But if method A is easier to
implement than method B, then (all other things being equal) method A
is better.


Couldn't agree more. I just think that your original base class was nearly there
for something that would handle any table, just given a list of fields to use!

Wonder how many months the total lifetime of this thread can be...

Matt
Jul 17 '05 #18
"Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
news:75******** *************** **@posting.goog le.com...
"Doug Hutcheson" <do************ *******@nrm.qld .gov.au> wrote in message

news:<B%******* ***********@new s.optus.net.au> ...
"Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
news:75******** *************** ***@posting.goo gle.com...
"Philipp Lenssen" <in**@outer-court.com> wrote in message

news:<bq******* ******@ID-203055.news.uni-berlin.de>...
> André Næss wrote:
>
> > Tony Marston:
> >

> > >
> > > I have condensed the arguments into a single article which can be > > > viewed at
> > > http://www.tonymarston.net/php-mysql/good-bad-oop.html
> > >

> >
> > I just think it's funny that you still don't understand object
> > composition. In your article you write: "How do you share code in OO > > systems? Through inheritance.", not even mentioning object
> > composition. Object composition was also the crux of my argument,
> > i.e.: where you see only inheritance, I see inheritance and
> > composition. From this we can only deduce that you in fact did not
> > properly understand my argument. That doesn't make the discussion any > > easier.
> >
>
> I was thinking the same. I saw the article, looked for "compositio n", > couldn't find it, and went away.

Just for you I have added a section on object composition. I hope you
like it.

http://www.tonymarston.net/php-mysql...tml#2003-12-05

Kiss, kiss

Tony Marston
http://www.tonymarston.net/


Tony,
A trifle defensive <grin>, but wholly correct. As another 25+ programmer, I can state without too much fear of contradiction that the customer pays me to solve his problem, not to write code which meets the approval of the
paradigm police.
More power to you, you rabid radical you!
Cheers,
Doug Hutcheson


People tend to describe me more as revolting than rebelling. Is there
a difference? :)

Tony Marston
http://www.tonymarston.net/


"Rebellent" , perhaps?
<g,d&r>
"8-)
Jul 17 '05 #19
"Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
news:75******** *************** **@posting.goog le.com...
Matty <ma*******@askm enoquestions.co .uk> wrote in message

news:<YN******* *************@w ards.force9.net >...
> "Tony Marston" <to**@marston-home.demon.co.u k> wrote in message
> news:75******** *************** ***@posting.goo gle.com...

<snip>

>>
>> http://www.tonymarston.net/php-mysql...tml#2003-12-05
>>


(Yet Another Follow Up...)

Can't help wondering what the object composition argument was, and how
on earth you could do it in a logical manner.

A table "has a" page of records?

A page of records "has a" table (what would it do if it didn't?)

Personally, yeah, I think composition isn't the way to do it...

/me thinks How about a table "has a" table perhaps???
;p

Matt


A table has 4 legs and a set of drawers. Now, if I were to drop the
drawers and spread the legs..... :)
Tony Marston
http://www.tonymarston.net/


Ah - a rebellent furniture fetish!
Strange fruit, Tony, strange fruit indeed.
"8-)
Jul 17 '05 #20

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