Re: Do people who use Ada also use ocaml or F#?

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Sun, 31 Oct 2010 16:07:10 +0100, Dmitry A. Kazakov  
<mailbox@dmitry-kazakov.de> a écrit:
>> You can build new components that use other components, hence you can
>> call it aggregation, but this is hidden in the body, so nobody cares,
>> it's not visible; unlike inheritance where the whole dependency has to
>> be visible.
>
> But reusable components are visible as well, e.g. a list [component 1] of
> arrays [component 2] of something [component 3].
Yes, they are also visible, but the visibility you need to have is not the  
same. Visibility here, does not really mean “what is visible”, instead it  
means “what needs to viewed”.

With composition, you just need to see the interfaces and what is directly  
connected to these interfaces, i.e. what you need to view is what is made  
of an exploration of the direct environment. With Inheritance, the  
exploration must be transitive, can go far and/or apply to many types,  
i.e. there is no real local circumscription of consequences, as what is at  
one place, may be visible from all the places where the inheritance graph  
can lead you from the original places (that is the meaning of “visible”  
here).

This can be powerful, as much as it can damage the whole system.

To talk using a picture : there are the kind of messages/mails/etc you  
will see no objection to broadcast, and there is the kind of you would  
avoid to. Something a bit similar applies (propagation). There are  
sensible things which should not be propagated through an Inheritance  
graph (which virtually has no limit), there are other for which you will  
not bother.

To say Composition is the only good way to go, would be extremist; but you  
can safely say, using Composition, you will avoid many potential troubles.  
The most secure you want to be with your design, the most you will use  
Composition. And if the power of Inheritance is used, you will have to  
carefully balance what you are throwing potentially far away (at least you  
may want to avoid for likely bombs, but you will not bother for fancy  
stuffs).

-- 
Si les chats miaulent et font autant de vocalises bizarres, c’est pas pour  
les chiens.