Re: Problem with limited with

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

"Jeffrey Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:kt0uo3$3kh$1@dont-email.me...
> On 07/27/2013 09:00 AM, Shark8 wrote:
>>
>> To be fair, the ONLY reason I have to use anonymous access types at all 
>> there
>> is because GNAT chokes up when I try to use the type itself. (I think 
>> there's
>> a comment to that effect elsewhere.)
>
> About the only thing you can do with limited with is declare access types 
> designating the types in the withed pkg, So of course an Ada compiler 
> complains if you try to do anything else.

Not true in Ada 2012. We realized that the language didn't need all of the 
restrictions on incomplete types that it had, and we removed a lot of them. 
See 3.10.1 and 13.14. The trick is that freezing a subprogram need not 
freeze the types of its profile -- that's only needed when there is a call 
or a body.

In particular, any incomplete type can be used as the name of a parameter so 
long as it is completed before the body of the subprogram is encountered. 
(The actual rules are a bit more complex than this, but this is the best way 
to think of it.) For limited with, this just means that a matching 
non-limited with has to be visible in the body of the package. As this is 
new, I can imagine that GNAT has bugs in this area. (I think the OP's code 
should compile, but I didn't check this in detail.)

The net effect is that you can use a type imported via a limited with 
without having any visible access types. (You can't have functions that 
return such types, or components, because those need to know more about the 
type than is available.)

                                                    Randy.