Re: Ada202X: Easy to use "UML private"-like components

[Shark8 <onewingedshark@gmail.com>]

On Sunday, June 23, 2013 7:12:53 AM UTC-6, Robert A Duff wrote:
> 
> 
> On the other hand, the private part kludge wouldn't be so bad if
> the syntax were different:

Perhaps something like this?

Package Example is
   Type Opaque is private;
private
   Type Opaque is separate COMPLETE_NAME;
   -- This flags to the compiler that the full type appears in the
   -- package body (as COMPLETE_NAME) and the public 'Opaque' is
   -- actually a pointer/reference/(not null access) to COMPLETE_NAME,
   -- also any primitive ops for Opaque are transitively private ops 
   -- of COMPLETE_NAME.
end;


>  The private part should be a separate
> syntactic compilation_unit, with its own with clauses, and should
> normally be stored in a separate source file from the visible part.

I don't know. Certainly for consistency's sake yes, but getting compiler writers to implement that as well might have been a death-knell for Ada 83.
Moreover, we would need some way to flag there isn't a PRIVATE area, like PRIVATE IS NULL; (Or conversely have the private section optionally in the spec, as it is now, but with PRIVATE IS SEPARATE as the trigger for an external private section.)


> There's an awful lot of horrible code duplication caused by the
> fact that the private part is in the same file as the visible part.

I'm not sure about that. Consider this:
Type K;

Type J is record
 Item : K; -- might need to be access K.
end record;

Type K is new Integer Range 0..100;

Sure "Type K" appears twice, but that's required so that we have some name for the type of J.Item. The items (full declarations) in the PRIVATE section are likewise.