• BLS (18/18) Mar 17 2006 Hi Don,
• Don Clugston (11/20) Mar 17 2006 Yes, that's exactly right. I'm saying that inheritance is rarely
• BLS (13/33) Mar 18 2006 Hi Don,
• Don Clugston (10/18) Mar 18 2006 I know the feeling. I'm an expat myself, and don't speak the local
• BLS (1/1) Mar 18 2006 Thanks Don !

"BLS" <lietz wanadoo.fr> writes:

Hi Don,

Don C. wrote :
<<In OOP, you spend your time trying to find Is-A relationships, but they
don't exist. Unsurprisingly, hardly anyone is "really" doing OOP. It
seems to be unimplementable.>>

Oops, what is the matter? . A Is-relation between two classes is just
inheritance. f.i. cB inherits cA, ergo cB is a special case of cA.


I think you talk about the problem to decide :  Do we have a
Has-Relationship or do we have a Uses-Relationship. ?!
I agree, it is often difficult to figure out the difference between Has- and
Uses- Relationship.
But when you keep in mind that a  Has-Relationship only exist when we can
say instead of :
cA has 2(n) cB objects ,
cA consists of 2 cB objects.
-------------------------
In other words : cA consists of 2(n) cB objects means  Has-Relationship.
Bjoern

Don Clugston <dac nospam.com.au> writes:

BLS wrote:
 Hi Don,
 
 Don C. wrote :
 <<In OOP, you spend your time trying to find Is-A relationships, but they
 don't exist. Unsurprisingly, hardly anyone is "really" doing OOP. It
 seems to be unimplementable.>>
 
 Oops, what is the matter? . A Is-relation between two classes is just
 inheritance. f.i. cB inherits cA, ergo cB is a special case of cA.

Yes, that's exactly right. I'm saying that inheritance is rarely 
appropriate. If you read the Design Patterns GoF book, you'll see that 

But the defining feature of OO design is inheritance. Without 
inheritance, OOP doesn't have polymorphism.

What I find extremely common in practice is "Can-be-treated-as-A" 
polymorphic relationships. Most of the time, "is-A" relationships are an 
approximation to "Can-be-treated-as-A" relationships. I think that 
polymorphism is very important, but inheritance-based polymorphism has 
many problems.

"BLS" <lietz wanadoo.fr> writes:

Hi Don,
okay, now I understand what you mean. Takes a while. You may have noticed
<g> that english is not my favourite language.
GoF.
Yes of course, I know about it. I read Bruce Eckel s Thinking in Pattern and
Prof. Moessenboek OOP in Oberon 2 instead because I have heard that GoF
Design Patterns is a bit too theoretical. Can you confirm ? Or will you say
it is a "You need it" book ?
Thanks,
Bjoern


"Don Clugston" <dac nospam.com.au> schreef in bericht
news:dveppu$1im5$1 digitaldaemon.com...
 BLS wrote:
 Hi Don,

 Don C. wrote :
 <<In OOP, you spend your time trying to find Is-A relationships, but


they
 don't exist. Unsurprisingly, hardly anyone is "really" doing OOP. It
 seems to be unimplementable.>>

 Oops, what is the matter? . A Is-relation between two classes is just
 inheritance. f.i. cB inherits cA, ergo cB is a special case of cA.

 Yes, that's exactly right. I'm saying that inheritance is rarely
 appropriate. If you read the Design Patterns GoF book, you'll see that

 But the defining feature of OO design is inheritance. Without
 inheritance, OOP doesn't have polymorphism.

 What I find extremely common in practice is "Can-be-treated-as-A"
 polymorphic relationships. Most of the time, "is-A" relationships are an
 approximation to "Can-be-treated-as-A" relationships. I think that
 polymorphism is very important, but inheritance-based polymorphism has
 many problems.

Don Clugston <dac nospam.com.au> writes:

BLS wrote:
 Hi Don,
 okay, now I understand what you mean. Takes a while. You may have noticed
 <g> that english is not my favourite language.

I know the feeling. I'm an expat myself, and don't speak the local 
language (German) as well as I'd like... Your English is about 100 times 
better than my German.

 GoF.
 Yes of course, I know about it. I read Bruce Eckel s Thinking in Pattern and
 Prof. Moessenboek OOP in Oberon 2 instead because I have heard that GoF
 Design Patterns is a bit too theoretical. Can you confirm ? Or will you say
 it is a "You need it" book ?

Well, GoF was the book that launched the Patterns movement, everyone 
quotes it all the term and uses terminology from it. A lot of the code 
in it isn't spectacularly good, and parts of the book seem a bit clumsy, 
but it was certainly groundbreaking. So, it's true that it's too 
theoretical, but I think it's still probably a 'you need it on your 
shelf' book. At least, you need a good idea of what's in it.

"BLS" <lietz wanadoo.fr> writes:

Thanks Don !