[BNE-PM] OO perl

[Don.Simonetta at mincom.com]

Well I've learned something new today - I'd never heard of Class::Contract 
until now. I've managed to track it down on cpan 
(http://www.cpan.org/authors/id/D/DC/DCONWAY/Class-Contract-1.00.readme). 
This sounds like it plugs a few of the deficiencies in perl's OO. Having 
only read a book on java and never coded in it, I would have said that 
java is nicer for OO. Especially in terms of syntax.

Tony, can you give a breif summary of object composition and aspect 
oriented programming? Is this a move away from one of the fundamentals of 
OO -namely inheritance?



>>They are both quite similar to use.  I haven't looked at how to do 
>>database connection pooling in dbi but it is quite easy now in java with 

>>jdbc2.  It can take more code in java to get some things done in perl 
but 
>>the object orientation in java is better than it was in perl.
>
>No, I'd say the object orientation in Java is not better in Perl. Try the 

>Class::Contract module, which gives you class invariants, abd true pre 
and 
>post conditions (and the pre conditions can refer to the previous state 
of 
>the object!). You can't do that in Java!

I'm hoping that pre and post conditions will come in to java in the 
future, 
some interesting work is being done in this regard under the title of 
Aspect Oriented Programming and a java implementation (AspectJ - 
www.aspectj.org) is available.

>(Java still doesn't have multiple inheritence - and don't tell me I don't 

>need it!)

I wouldn't presume to tell you that, I will tell you, however, that I 
don't 
need it... :-).  An interesting perspective on inheritance that is being 
stated by a number of the OO gurus is that when designing we should favour 

Object Composition over Inheritance which in my view diminishes the 
arguments for multiple inheritance.  Aspect Oriented Programming gets 
around some of the issues one would solve with multiple inheritance by 
providing "aspects" that stripe different functional areas of an 
application.



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