Re: Self pointer in limited record

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sat, 01 Sep 2007 16:15:44 +0200, Georg Bauhaus wrote:

> Dmitry A. Kazakov wrote:
>> On Sat, 01 Sep 2007 15:33:09 +0200, Georg Bauhaus wrote:
>> 
>>> (The true O-O programmer might suggest that we should simply
>>> pass an additional object-as-module parameter to every
>>> package subprogram... )
>> 
>> Yes, it is better to keep packages stateless.
> 
> Though by using tagged objects for a module
> and not a stateful package, you will dismiss a few
> properties of packages that can be helpful when
> modeling singleton modules:
> 
> 1 - If there is just one object in the problem domain a
> package is a perfect match and will be straight forward, safe,
> and simple to implement. No need to worry about static and
> dynamic scopes of module-objects passed around because
> there is just this one named package for the problem
> domain object.

Yes, yes, but this is a different case. Dealing with singletons, I probably
would use a [stateful] package instead of objects. Types presume multiple
instances of. Singleton in OO breaks this concept. Ada offers a cleaner
alternative. Why should we force it into a type? Let it be a package.

I think the empiric rule could be: if a package is used to declare types,
then it should have no mutable state. Otherwise it should not have type
declarations.

> 2 - Nesting packages is an option, a distinguishing feature
> of Ada IMO; a package nested inside a subprogram is a
> simple solution to the life cycle problem of module style
> objects.

Hmm, a subprogram has all properties of a package. So there is no obvious
reason why nested package (except instances of generic packages, of
course), might be useful there.

BTW, I guess child and separate packages might probably replace nested
packages. Excluding generics, I mean. Maybe if there were no generic
packages we could drop them altogether.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de