Re: limited agregate and limited components default initialization

[Jere <jhb.chat@gmail.com>]

On Saturday, March 31, 2018 at 8:52:39 PM UTC-4, Jere wrote:
> On Saturday, March 31, 2018 at 7:36:59 PM UTC-4, Jean-Claude Rostaing wrote:
> > Why does a component declaration like that:
> > type Item_Accessor (Item: not null access Item_type) is limited record
> >       Ref: Item_access := SET(Item_Record'(Item => ITEM.all, others => <>));
> >    end record;
> > unconstrained subtype in component declaration
> > ? ITEM is limited but IS constrained by the default initialisation
> > It forced me to add the function DEFAULT_INITIALIZATION as a parameter, which I would prefer to not to. But since the result is the same, I'll drop it.
> > Item (and the article it is in) is never meant to be left uninitialized.
> > 
> > Also, how to get rid of the problem with
> > function Set (Value: in Item_type) return Smart_Pointers is
> >      (Smart_Pointers'(Controlled with Node => new Accessor_type'(Data => new Item_type'(Value), Count => 1)));
> > which gives :Initialization not allowed for limited types.
> > So an aggregate like this is not counted as a "limited agregate" ??
> 
> I may be misunderstanding you, but if Item is a limited type with a default
> discriminant, it is "unconstrained" since the ada compiler cannot know
> at compile time what the actual size will be.
> 
> See:
> https://gcc.gnu.org/onlinedocs/gnat_rm/The-Size-of-Discriminated-Records-with-Default-Discriminants.html

Actually, the limited might make it ok, but I seem to remember it still being 
considered unconstrained from a language point of view.  Perhaps a language 
lawyer type can make a better comment.