Re: Possible Ada deficiency?

["Ed Falis" <falis@verizon.net>]

On 1 Jan 2005 19:36:37 -0800, <danmcleran@hotmail.com> wrote:

> Because by using access values, one would have to manage the memory
> associated with the object. Also, a dangling reference could be left
> behind. See Jeff Carter's post:
>
> http://groups-beta.google.com/group/comp.lang.ada/browse_frm/thread/93d7def3eeefbc26/e8e7d2d6f3847f5c#e8e7d2d6f3847f5c
>
> IMO, a proper construct to allow hiding of implementation detail from
> child packages is superior to this suggestion.
>

IMO, the kind of type opacity you're looking for here is rarely enough  
used that an additional language feature is unjustified.  As others have  
pointed out, child units are most often used to provide enhancements or  
additional facilities to a basic abstraction. Sometimes/often this needs  
access to the underlying representation.

If you read the introductory section on hierarchical libraries in the Ada  
95 Rationale, (II.7), I think you'll find that one of the main motivations  
(if not the main motivation) for the concept is to facilitate the sharing  
of private type representations among related abstractions.  In that  
context, the kind of type opacity you want is a corner case, addressable  
by other facilities of the language in a "building block" manner - the  
usual Ada way of addressing non-language-defined capabilities.

This may sound conservative, and it is - there is always a cost related to  
adding new features to the language.  In this particular case, we have to  
agree to disagree about the relative value of the proposed construct.

- Ed