Re: Properties

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

On Wed, 1 Dec 2010 15:21:39 +0000 (UTC), Warren wrote:

> I haven't looked at 
> GtkAda in years, but my early version opinion of it was that 
> it seemed too much like bending a C library into Ada terms.

Yes it is.

> A library designed in Ada from the ground up, would be better.

But we cannot, think about a type- and task-safe notification mechanism. I
have no idea how to do it without tagged tasks and protected objects. And I
don't want to instantiate a generic each time I need an event handler. And
I do want the compiler to check that all events are handled.

> Part of the difficulty is that something like a GUI takes so 
> much effort to develop. To get one developed to a "standard 
> level" would likely require some level of sponsorship. 
> Especially if you want to also attempt to make it platform 
> neutral.

The main problem is the interface of such a library. There are multiple
parallel hierarchies need to be handled: a hierarchy of widget types, a
hierarchy of widget containers, a hierarchy of event handlers (events are
filtered, propagated, swallowed, re-generated). At least the first and the
third must be statically checked, if we really want it be Ada. Very likely
that some composite widgets (the second hierarchy) should also be static.
Then there is a fourth hierarchy of widget properties. Some of the
properties are inherited from parent types, some are from parent
containers.

All these hierarchies must play with each other. Ada's type system is not
mature for this.

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