Re: limited agregate and limited components default initialization

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

On Saturday, March 31, 2018 at 10:40:22 PM UTC-4, Jere wrote:
> On Saturday, March 31, 2018 at 10:07:20 PM UTC-4, Jean-Claude Rostaing wrote:
> > --
> > -- Item_type and ITEM_RECORD are NOT meant to be declared uninitialized, ever.
> > -- So how do I tell this to GNAT so that Item: aliased ITEM_TYPE as a component is allowed ?
> > -- Implementing List_type with common access types and "type Bla, type Blabla is access Bla, complete declaration" would have been easy, but the private type Smart_Pointers made a hell of it.
> > 
> > with Pointers;
> > 
> > generic
> >    type Item_Type(<>) is limited private;
> > package Lists is
> >    type List_Type is limited private;
> >    type Item_Accessor (Item: not null access Item_type) is limited private with Implicit_Dereference => Item;
> >       function Get(Position: in List_Iterator) return Item_Accessor;
> > private
> >    type ITEM_ACCESS;
> >    type Item_Record is limited
> >       record
> >          Item: aliased Item_type;
> >          Next : Item_Access;
> >          Pred : Item_Access;
> >       end record;
> >    package Record_Pointers is new Pointers (Item_type => Item_Record);
> >    type Item_Access is new Record_Pointers.Smart_Pointers;
> > 
> >    type Item_Accessor (Item: not null access Item_type) is limited record
> >       REF: ITEM_ACCESS := SET(ITEM_RECORD'(ITEM.all, others => <>));
> >    end record;
> > 
> >    type List_Type is limited record
> >       First: Item_Access;
> >       Last : Item_Access;
> >       Count : Natural := 1;
> >    end record;
> > end Lists;
> > 
> > And what I was pointing your attention at was:
> > lists.ads:39:49: initialization not allowed for limited types
> > for: REF: ITEM_ACCESS := SET(ITEM_RECORD'(ITEM.all, others => <>));
> 
> Ok, your problems:
> 1.  For  your Item_Record type, the parameter Item, cannot be of type
>     Item_Type as it is unconstrained.  That is what gives you the first
>     error
To clarify because I typed that horribly:  Item_Type cannot be an 
unconstrained type if you wish to make it a component of a record.
It needs a constraint.  That's why you have to remove the (<>)
in your generic formal for Item_Type.