Re: How to return an empty aggregate

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

On 4 Kwi, 17:38, george.p...@gmail.com wrote:

> Good example is a factory.  Should it have a
> mechanism to register-unregister itself?

Not necessarily. I might be as well selected at startup time by some
other entity (in which case it is also a strategy).

> In addition such
> objects make sense in singleton form

Yes and no.
Yes, because it does not make any sense to destroy them and create
again.
No, because it is *not harmful* to destroy and create them again (see
also the monostate pattern):

F : Factory'Class := Make_Funny_Factory;
Obj : Object := F.Make_Object;

Above, factory F is a transient entity that is used just to create one
object. It might be a singleton as well, but does not have to.

> and likely involve some sort of
> guarding mutexes or be implemented as protected or tasks.

If it's stateless, then it does not need any protection - there is
nothing to protect.

> BTW in C++
> empty factory class will be fine due to implied constructor/
> destructor.

The empty factory class will be fine in Ada as well.

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com