Re: Naming of Tagged Types and Associated Packages

["Jean-Pierre Rosen" <rosen.adalog@wanadoo.fr>]

>And whatever you do, please do NOT name a type "Object" or "Instance".
>This is a sure sign of confusion about the difference between a module
>and a type, which are orthogonal language features in Ada.
>
Well, since I was the first one to publish that notation (I do not claim to
be the first one who thought of it), let me follow up.

We are talking about classes here, and a class is an encapsulation of a data
type together with operations. In that sense, a type is certainly not a
class, since it addresses only the data-type part of a class.

Rather, a class is a certain way of using a package, to declare a type and
associated operations (methods), and nothing else. Of course, there are
other ways of using packages: packages, as well as types and nearly any
other feature of the language, are building blocks that allow you to create
various paradigms depending on the way you put them together.

However, if you agree that such a package corresponds to what is called a
class in OO languages, then it makes sense to name the package, not the
type, after the entity you want to represent. Now the package may declare
some utility types in addition to the "main" type; it makes sense to have
some notation to distinguish this main type. "Instance" or "Object" look
nice in a declaration like:
    My_Account: Bank_Account.Instance;

but this is not the main point. The really important point is to use the
same name for the main type of every  "class package", because it allows you
to have a uniform convention, whether you're using a declared package or an
instantiation of a generic. And remember that generic are very important,
since they provide multiple inheritance (or to be more politically correct:
because they fulfill the needs that are fulfilled by multiple inheritance in
other languages ;-)

A full discussion of these issues can be found in the paper "a naming
convention for classes in Ada 9X" which appeared in Ada Letters by the end
of 94 (sorry, I don't have the exact reference at hand).