Re: Idiom for a class and an object in Ada

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

On Tue, 19 Oct 2004 11:40:08 -0400, Matthew Heaney wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:138j4nfhzsc45$.1581kzqfi5e89$.dlg@40tude.net...
>> On Tue, 19 Oct 2004 10:44:04 -0400, Matthew Heaney wrote:
>>
>>> The term "class" in Ada has a very specific meaning.  In Ada, it means
>>> "family of types."  Specifically, it means "family of tagged types, 
>>> having
>>> this common ancestor."
>>
>> This is incorrect. For example ARM 12.5 refers classes of types other than
>> "class rooted in".
> 
> Yes, of course it does, but that's obviously not what we're discussing here, 
> since the OP isn't using the term "class" in the sense of "class of integer 
> types," etc.
> 
> We simply need to clarify whether we're talking about a specific type T, or 
> a family of types rooted at T, namely T'Class.

[ BTW, to be even more pedantic (:-)), T'Class is not a family of types. It
is *a* type, which is a closure of that family. ]

Anyway, I see nothing criminal in the package name "AD_Converter_Class".
The names should reflect the application domain, rather than language
gears. With some minor exceptions, which IMO always more or less reflect
language deficiencies (I mean XXX_Ptr, XXX_Type etc), Hungarian notation
and company is an evil thing. I have no problem to read AD_Converter_Class
as "a class of physical devices, described in general by this package".
Whether that class is mapped to a type or to a class of related types is a
design decision.

But the original question was how to name the ultimate instances of that
type or types of a family, including generic case, sets of derived types,
constrained subtypes, whatsoever. The idiom should not depend on where the
instances come from. So important is only (if I correctly understood
Marin):

1. Instances are statically known
2. Instances should be public
3. Instances should have unique names (no arrays of, no containers of, no
factories of)

My personal preference is (b) - child packages. When necessary, one can
additionally create an assembly package with renames of converters
instances from different packages:

with AD_Converter_Class.Diamond;
with AD_Converter_Class.AX10410A;
...
package AD_Converter_Class.This_Board_Hardware is
   AD_1 : AD_Converter_Class.Diamond_MM.AD;
   AD_2 : AD_Converter_Class.AX10410A.AD;
   ...

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