Re: [Revisited] How to get around "access type must not be outside generic unit"

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

On Wed, 24 Jan 2007 14:50:49 -0600, Randy Brukardt wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:1u2mhr9ypij4u.bn3yayn7o9l3$.dlg@40tude.net...
> ...
>>> But in any case, the solution to your problem (as always) is to put the
>>> 'Access into the private part of the specification. Do that with an
>>> appropriate constant declaration. (If the parameter type of Register was
>>> anonymous, there is no problem, so there must be a named type that can be
>>> used.) Doing so will force the generic to be instantiated at the library
>>> level.
>>
>> OK, that's definitely better than Unchecked_Conversion. In Ada 95 it was
>> enough to add a declaration of the subprogram to the specification, now we
>> also need an access object. This is strange, at least not obvious. Why
>> should it change anything?
> 
> Because it's part of the contract model.
>
> That is assume-the-best in the
> visible part of the spec, and assume-the-worst in the body. (We're somewhat
> confused about the private part.) Whenever we assume-the-best, there is a
> required recheck in the instance.
> 
> Thus, putting such a 'Access in the spec means that it will be rechecked and
> rejected if it causes trouble. In this case, that means that the generic
> will be rejected if it is instantiated in a nested scope. 
 
Hmm, I don't think it is a contract. To be a contract "I want X'Access"
should be in the generic formal part. It is closer to how C++ templates
work. (for "I want X'Access" there even exists a reserved keyword)

But that's no matter.

>> I mean, if it is semantically correct, then why
>> the compiler cannot deduce it? Is it semantically correct? In the case with
>> Glib above, would it be possible to instantiate a generic package in a
>> local scope; call to Boxed_Type_Register_Static passing a constant as you
>> described; and then leave the scope?
> 
> No, the instance will be rejected at compile-time as failing an
> accessibility check.
[...]

I see, thank you for explanation.

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