Re: Custom model in gtkada?

[Stephen Leake <stephen_leake@acm.org>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Thu, 22 Jun 2006 09:16:22 +0200, Emmanuel Briot wrote:
>
>> Dmitry A. Kazakov wrote:
>>> I would expect callbacks be primitive operations of a tagged type rather
>>> than pointers.
>> 
>> This is of course a design choice, and you can easily implement a small
>> layer on top of GtkAda to do just that.
>> The advantage with pointers is that you can add or remove callbacks during
>> the life of a widget, which is harder to do with primitive operations where
>> you need flags to know whether to react to the event or not. Also you can
>> have multiple callbacks on the same signal, which, again, is harder to do
>> with primitive operations.
>
> Maybe, though I doubt that events were a right design decision (as a
> notification mechanism).

How many GUI programs have you written? With how many different toolkits?

I've used Visual Basic (essentially tagged, I think :), Borland's C++
framework (tagged/dispatching), Windex (Ada tagged), GWindows (mixed
tagged/pointers), and Gtk (pointers).

I think Gtk is the best model, although the C underpinnings make
things difficult sometimes. In particular, it is difficult to detect
some errors at compile time, that the fully Ada systems can detect. At
root, the C pointers are not strongly typed.

> Another point, a list of pointers to subprograms is in no way better than a
> list of tagged objects (with primitive subprograms).

Why?

I would find a list of tagged objects confusing.

-- 
-- Stephe