Re: Seeking for papers about tagged types vs access to subprograms

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

On Fri, 10 May 2013 20:00:39 -0500, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
> news:1q07vm77kfwla$.1cz0xwxspxhay.dlg@40tude.net...
>> On Thu, 9 May 2013 16:33:55 -0500, Randy Brukardt wrote:
>>
>>> As usual, I pretty much totally disagree with your thinking here. The last
>>> statement is trivially true, of course, but so what? A program has to be
>>> built on top of a handful of "big" abstractions. And for each of those "big"
>>> abstractions, there has to be a single type which takes the lead 
>>> (probably with a family of other types in support).
>>
>> Takes the lead, how? An abstraction including Employer, Employee, Factory,
>> Salary, Time, Duration, Integer, Address, Gender, Age ... Who takes the
>> "lead"?
> 
> The container that wraps those things up, of course. And if there is no 
> container, then they're clearly all separate abstractions that have to be 
> treated that way.

How to separate Employer and Employee?

>>> In bigger systems, each of those abstractions corresponds to a subsystem 
>>> (in Ada, that's best modeled as a family of child packages). Inside each of
>>> those subsystems, you'll have another family of types. But the majority of
>>> these types should not extend beyond the subsystem.
>>
>> How these subsystems are going to interact to each other?
> 
> As little as possible.

It does not tell how.

>>> You seem to claim that all types are equally important, which is obvious
>>> nonsense.
>>
>> Yes, I say that unimportant types need not to be exposed in public
>> interfaces.
>>
>> Everything declared in the *same* scope is equally important, or else you
>> have a design issue.
> 
> What utter nonsense.
> 
> Ada.Text_IO defines Count, File_Type, File_Mode, Field, and Number_Base 
> types. If you think these are all equally important for the primary task of 
> doing I/O, you have a real problem with perspective. File_Type does all of 
> the work, while the rest just raise the abstraction level a bit.

In which sense? From the implementation point of view GNAT's File_Type is
an address or integer, if I correctly remember. It does nothing. From the
user's point of view Put_Line, Get_Line do not even mention File_Type. And
there are lot of questions to Text_IO design anyway. One problem is worth
mentioning. It is a typical God-class design:

   http://en.wikipedia.org/wiki/God_class

This is the destination point of the idea of equivalence of object and
abstraction, a very OO idea. What you are talking about is basically
classic OOA/D put in different terms.

> I don't see any reason to quantify "importance".

In order to prove your point?

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