Re: How to transfer Class-Wide object to a Task ?

[William FRANCK <william.franck@free.fr>]

Thank you Shark,
I'll give it a try too :-)

And send you all a more complete source code of my use case.

William


On 2019-10-14 21:57:57 +0000, Shark8 said:


> On Monday, October 14, 2019 at 2:21:50 PM UTC-6, William FRANCK wrote:
>> On 2019-10-14 19:41:53 +0000, William FRANCK said:
>> 
> Maybe something like this:
> 
>     procedure Example is
>         Package Types is
>             Subtype Params is Ada.Streams.Root_Stream_Type'Class;
>             Type Root   is abstract tagged null record;
>             Function Create (Parameters : not null access Params) 
> return Root is abstract;
> 
>             Type Circle is new Root with record
>                 Radius : Float;
>             end record;
> 
>             Type Square is new Root with record
>                 Side : Integer;
>             end record;
>         Private
> 
>             Function Create (Parameters : not null access Params) 
> return Square;
>             Function Create (Parameters : not null access Params) 
> return Circle;
>         End Types;
> 
> 
>         Use Types;
>         Package Class_Holder is new 
> Ada.Containers.Indefinite_Holders(Root'Class);
>         Task Type Producer( Stream : not null access 
> Ada.Streams.Root_Stream_Type'Class ) is
>             Entry Get( Object: out Class_Holder.Holder );
>         End Producer;
> 
>         Task body Producer is
>             Function MAKE is new Ada.Tags.Generic_Dispatching_Constructor(
>                T           => Types.Root,
>                Parameters  => Ada.Streams.Root_Stream_Type'Class,
>                Constructor => Types.Create
>               );
> 
>             Function To_Tag return Ada.Tags.Tag is
>             Begin
>                 Return Square'Tag;
> --                  (if    Ch = 'C' then Circle'Tag
> --                   elsif Ch = 'S' then Square'Tag
> --                   else raise Constraint_Error with "Tag '"&Ch&"' is 
> invalid.");
>             End;
> 
>         Begin
>             accept Get (Object : out Class_Holder.Holder) do
>                 Object:=
>                   Class_Holder.To_Holder( MAKE(To_Tag, Stream) );
>             end Get;
>         end Producer;
> 
>         Function Get(P : Producer) return Root'Class is
>             H : Class_Holder.Holder;
>         Begin
>             P.Get(H);
>             Return H.Element;
>         End Get;
> 
> 
> 
>         Package Body Types is
>             Function Create(Parameters : not null access Params) return 
> Square is
>             Begin
>                 Return (Side => 3);
>             End;
> 
>             Function Create(Parameters : not null access Params) return 
> Circle is
>             Begin
>                 Return (Radius => 2.2);
>             End;
>         End Types;
> 
>     begin
>         Ada.Text_IO.Put_Line( "START EXAMPLE." );
>         declare
>             I : Ada.Text_IO.File_Type renames Ada.Text_IO.Standard_Input;
>             P : Producer( Ada.Text_IO.Text_Streams.Stream(I) );
>             O : Root'Class := Get(P);
>         begin
>             Ada.Text_IO.Put_Line( "Tag: " & Ada.Tags.Expanded_Name(O'Tag) );
>         end;
>         Ada.Text_IO.Put_Line( "STOP EXAMPLE." );
>     end Example;