Re: Indefinite Containers of Indefinite Private Types

["Randy Brukardt" <randy@rrsoftware.com>]

"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:mpr8rn$33n$1@dont-email.me...
> On 08/04/2015 01:47 PM, Randy Brukardt wrote:
...
>> One could imagine having a declaration for the generic (perhaps an 
>> aspect?)
>> that would allow such instantiations (and disallow such objects), but 
>> again
>> there has been little traction for such proposals, all of which are quite
>> complex to describe and implement.
>
> I can guess so. Probably a new generic formal type would be desired. 
> Meanwhile
> I'll put up with the noise.

That's one possibility. We could call it a generic private type. Oops --  
that name is taken, and alternative names are annoying. (The idea of course 
would be similar to the generic incomplete type; the restrictions on the use 
of a private type would be enforced on the uses of the generic formal type.)

We've also looked at declarations (maybe an aspect) for the generic as a 
whole, there was a proposal for a "forward" declaration for the generic 
(that is, you'd be able to separate the visible part of the generic from the 
actual instance, just like in other kinds of packages), and a proposal to 
change the freezing to be exactly like a macro (meaning a break in the 
contract model, and a horror to implement on top of that). We also found 
that there is a workaround of sorts using a child package to hold the 
instantiation, which works so long as the private type doesn't use something 
from the instantiation (usually a cursor for a container) in its full 
declaration. The existence of the workaround lowers the priority of finding 
a fix, and given the difficulty of doing so, we pretty much gave up. I'm 
sure we'll revisit it someday.

                                                     Randy.