Re: Callback in Ada

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 27 Lis, 11:22, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:

> There are alternatives to callbacks; for example I believe Claw and Qt
> use overriding primitive operations instead of callbacks.

YAMI4 uses this approach for delivering messages and various
notifications.
AWS uses this, too.

You have left that at the end of the list as if it was the least
capable option, but I think that callbacks implemented this way (in
particular with interfaces) have several important advantages:

1. They can be stateful. Procedure callbacks can refer to enclosing
state as well, but for example having an array of stateful callbacks
is less obvious. Interfaces can do that.

2. They are composable. A single entity can implement many callbacks
and this can be enforced at the level of type system, not by mere
convention.

3. Last but certainly not least: they can be implemented directly as
protected or task objects.

I would not use them for the passive iterator idiom, but for any form
of asynchronous delivery, they can be very powerful.

--
Maciej Sobczak * http://www.inspirel.com