Re: Top 10 Worst C# Features

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

On Thu, 3 Sep 2015 14:00:52 +0200, G.B. wrote:

> On 03.09.15 13:39, G.B. wrote:
>>> An object of a type is *same* in all contexts, because the type is same.
>>
>> While an object doesn't change either identity or type,
>> it does changes state. This is an event, too.
> 
> Seen from a different angle:
> What could a type system have to offer to GUI programming?
> Some kinds of "event" are as ubiquitous in GUI programming
> as they are essential. Can this be made static?

Yes it can. See below.

> AFAICT, today we have string literals identifying things
> that can be called (Gtk), or we have selectors (Objective-C)
> for a similar thing, etc.

GtkAda has typed events on top of untyped Gtk events. The problem with it
is that it is reversed. The interface is of the button, e.g. it is the
primitive operations of the button (e.g. On_Button_Clicked), which is
useless in most cases. It should have been of the widget handling button
events:

   Button ---------event----------> Handler widget
    |
   On_Button_Clicked

The operation, and types hierarchy, must be on the right. The controlling
parameter is not Button but the handler widget.

> A mouse click or gesture is thus
> another kind of event to which programmers might want to attach
> something that reacts. How would static type systems help,
> knowing that trying to make them help has allegedly failed
> in the past?

The design is that you have a handler interface, e.g. of a button events
handler with the primitive operations of event notifications. The widget
catching button events implements this interface. Note that differently to
Ada or C++ interfaces this one is additive. I.e. if you handle more than
one button, the inherited interfaces of do not coalesce. Other examples of
this type of inheritance is doubly-linked list header, queue element etc.

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