Re: How to return an empty aggregate

[george.priv@gmail.com]

On Apr 4, 4:35 pm, Maciej Sobczak <see.my.homep...@gmail.com> wrote:
> 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.

To me it seems that simple callback will be much more simple and clear
way to achieve the same result.

type Make_Object is access function(Context: Contect_Type) return
Object;

Obj : object := Make_My_Object(Some_Context_Selector);


>
> > 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.

except for reenterance that in most of cases matter for that type of
objects.

>
> > 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