Re: Deligation with Ada95

[Lao Xiao Hai <laoxhai@ix.netcom.com>]

Hans-Olof Danielsson wrote:

> Hi,
>
> Some experts state that _deligation_ is a technique used in OOP
> to avoid subclassing reducing the complexity of a system. If some
> of you know recourses, other than ACM Ada Letters, Nov/Dec
> 1994, covering this technique applied with Ada 95,
> would you please apoint me those other recources.

The best example of delegation in Ada 95 is the requeue.   In
delegation,
one object asks another to do the actual work requested of it.   That
class
can then forget about the delegation.   The delegated class can respond
directly to the original requestor.   This is not like a procedure call
where
the original request must unwind through a stack.   It is not like an
entry
call where the request is kept on the queue of the accept statement.
The
actual requeue does not block the delegator the way an entry call would.

There are actually very few languages that implement this idea directly.

C++, in its first design, was intended to include this feature, but it
was
eliminated for some reason.

Richard Riehle
AdaWorks Software Engineering
richard@adaworks.com