From: Robert Klemme <shortcutter@...>
Date: 2008-12-07T21:48:44+09:00
Subject: Re: class vrs. method

On 07.12.2008 11:58, Tom Cloyd wrote:

> I'm getting it done by writing a number of methods. I keep looking at 
> other people's programming, and I see many, many classes. Some of these 
> classes look pointless to me. A mere method would have done the trick. 
> Why a "class"? I personally feel no need whatsoever to actually USE one. 
> I'm getting everything done easily and artfully with mere methods. I 
> simply don't get it - about classes. It looks like an elegant idea, and 
> in more complex programming I can imagine why one might use them, 
> but...I've simply cannot find a reason to bother.
> 
> I've read a lot about them, but...here's my question:
> 
> Am I missing something? Can anyone give me a compelling reason to write 
> fewer methods and more classes?

Interesting question and not easily answered - at least not in 10 words.

For me, the main advantage of OOP over procedural programming is 
encapsulation - or to name a different term "abstract data types": you 
combine state (variables) and all the legal operations that can be 
applied to it - excluding all illegal operations at the same time.  This 
leads to more robust code because, if all classes do only one thing and 
do that well, you can more easily reuse the code and also the structure 
is much easier to grasp for someone else (or for you, if you find you 
need to change something a few months later).

Classes simply give you at least two more dimensions in which to 
structure your code via encapsulation and inheritance. (Although I 
personally feel that inheritance is overrated and often overused.)

If you are really interested in the matter and are ready to spend some 
time (and money) I recommend reading "Object Oriented Software 
Construction" by Bertrand Meyer (often called "OOSC").  It's a big book 
but you can read it one concept at a time.  And although he writes 
mostly about Eiffel (although it is mentioned at most once) he merely 
talks about all the concepts related to OOP - which happen to be present 
in Eiffel.  IMHO Eiffel is the language which contains the richest set 
of OO related features.  BM certainly is among the guys on this planet 
with the best understanding of what OO is about.

> If anyone's interested, the program to which I referred may be examined at
> 
> http://tomcloyd.com/misc/setnet.txt

An easy way to "find" your classes are CRC cards.  "CRC" means "class 
responsibility collaboration".  Basic idea is to identify things that 
could be classes, write down their responsibilities and other classes 
they should collaborate with.

If I were you I would at least create a class Database with all the 
legal operations (e.g. open or read, close or write, add_relationship 
etc.).  I did not look closely enough to decide whether I would want to 
have one database with all the nodes, relationships and links in it but 
chances are that I would choose that approach.  The reason is, that you 
want one set of data which is _consistent_.  (Btw, you could also build 
your database on top of PStore which guarantees some transactional 
consistency - you won't be able to manipulate the DB via editor though.)

Maybe I would also have a class UserInterface which deals with all the 
ways a user can interact with your Database.  Looking at method 
show_help this could be made easier (and more efficient at the same 
time, although this is probably not important here) by placing all the 
help messages in a Hash.  I would also try to keep methods much shorter. 
  For example, you have a big main loop in method main where you do all 
sorts of things some of which you could refactor to another method or 
even class (parsing of the command line for example).

Kind regards

	robert