Re: Package's private parts and protected types

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Stephen Leake <stephen_leake@stephe-leake.org> writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
>
>> Adam Beneschan <adam@irvine.com> writes:
>>
>>>...And that
>>> issue exists with GNAT also---you delete some files from your
>>> directory with a wildcard, somehow foo.adb accidentally gets deleted
>>> along with them, and the compiler still thinks your program is OK.
>>
>> Seems unlikely.
>
> Which means it will be very hard/confusing to debug when it does
> happen, since you will not be familiar with the problem. So it is
> important for the tool to handle the unlikely situations nicely.

I suppose...

>> Here's a similar issue: One reasonable design pattern is to have
>> a body that contains a type extension, which registers itself
>> into some global data structure.  All calls to this thing
>> are indirect (via the parent's 'Class).  Nobody needs visibility
>> on this thing, so its spec is completely empty, except for
>> the obligatory pragma Elaborate_Body.  Unfortunately, if you
>> forget to 'with' it, it will be silently ignored.
>
> And if you do 'with' it, GNAT will complain that it's unnecessary, so
> you have to put a pragma Warnings (off) on it. QtAda does this for
> some stuff; it's annoying.

But that's a hugely useful warning.  Without it, you end up with
useless 'with's accumulating in your code.  An occassional
pragma Warnings is well worth the trouble, IMHO.

> I prefer to handle that case by making the registration function
> visible in the package spec, rather than calling it in the package
> body execution part. Then the main program has to call it, and no
> compiler warnings are generated.

Self-initializing packages are a Good Thing, I think.

I often do it like this: The parent type is limited controlled,
and Initialize/Finalize install/remove the object into some data
structure.  The derived type just overrides some primitive
ops (not Initialize/Finalize), and declares one or more
objects -- all in some package body.

- Bob