General talk about software patterns

[Ekárt László <Ekart.Laszlo AT evosoft.hu>]

        Hi, there

> An original point of view, probably. But it's not always bad to be
> original :) I understand your point of view about inheritance abuse.
> However, I still think that Template Method is probably the most useful
> pattern: 1) it's the cornerstone of many patterns, including the Observer
> you put on the top ! 2) Template Method in fact doesn't requires
> inheritance,you can use it even within the same class, and it does still
> make sense.
I agree. I made a mistake. The template method is useful just do not abuse it 
trough inheritance. It can be used I have used it, but I have seen systems 
that abused inheritance and template method was present in this systems very 
heavily.

> >Other pattern that I use extremely often is the decorator. This is
> because I tend to work in a bottom up XP style sometimes. If >you work in
> top to bottom way you shall have strategy patterns instead.
> 
> Can you explain ? I've always assumed that through refactoring, the XP
> design still leads to "normal" design. In my point of view, it's the TDD
> which leads to design specifics, including strong classes insulation with
> interfaces, in order to make the system testable piece by piece ...

Here is how I proceed: Write a class that fulfils a specific functionality. 
It is good for the moment or for that iteration. Later on I want to add 
functionality but I do not want to break the cohesion of the first class. So 
I add the functionality as a decorator class. I use aggregation instead of 
inheritance so it is like adaptor. I "delegate" the methods that I need from 
the first class.
You can use Mixins instead of Decorator when you add the new functionality 
and refactor later in a better way. I do not know which is better, time will 
tell. :-)

When you are thinking from the other way, than you will add new specific 
functionality to a more generic class by strategy. (Top-down)

That is all.

Best regards,
Ekart Laszlo