Re: allocators for classwide types?

[Ted Dennison <dennison@telepath.com>]

Ted Dennison wrote:

> Robert A Duff wrote:
>
> > > Gnat actually generates a compiler error on my variant of this. ...
> >
> > You should post the text of the message.
>
> It was an internal Gnat error. That's obviously a bug, of course. But 95% of
> the time those are caused by my doing something illegal in a way that the
> compiler didn't expect. It looks like in this case I may have been doing

OK. After further playing around, it appears the problem was actually a convoluted
parameter naming problem; not really anything to do with classwide types at all.
In my actual code, the package "Get" existed in was a generic child package of
package_1, which itself was a generic. The second parameter happened to be named
the same as the parent package. It also happened to be named the same as the
record field it was getting allocated and placed into. I expanded my toy example
to match:

-----
generic
   type Fred is (<>);
package Package_1 is

   type Instance is tagged record
      Fred_Field : Fred := Fred'First;
   end record;

   subtype Class is Instance'Class;
   type Handle is access all Class;

end Package_1;
package Package_2 is

   type Instance is tagged null record;
   subtype Class is Instance'Class;
   type Handle is access all Class;

end Package_2;
with Package_1;
with Package_2;

generic
   Max_Fred : in Fred := Fred'Last;
package Package_1.Classwide_Allocator is

   type Descriptor is record
      Field_1 : Package_1.Handle;
      Field_2 : Package_2.Handle;
   end record;

   function Get (Package_1 : in Package_1.Class;
                 F2 : in Package_2.Class
                ) return Descriptor;

end Package_1.Classwide_Allocator;
package body Package_1.Classwide_Allocator is

   function Get (Package_1 : in Package_1.Class;
                 F2 : in Package_2.Class
                ) return Descriptor is
   begin
      return (Field_1 => new Package_1.Class'(Package_1),
              Field_2 => new Package_2.Class'(F2)
              );
   end Get;

end Package_1.Classwide_Allocator;
----

The above complains on the declaration of Get about an attempt to use Package_1
before the child package is complete. Obviously its confusing Package_1 the
parameter with Package_1 the package. Is this what its supposed to do? I suspect
so.

But lets add one more wrinkle that my full program has. Package_1 (and thus its
child) are actually themselves children of another package:

----
package T is
   Global : constant := 3;
end T;
generic
   type Fred is (<>);
package T.Package_1 is

   type Instance is tagged record
      Fred_Field : Fred := Fred'First;
   end record;

   subtype Class is Instance'Class;
   type Handle is access all Class;

end T.Package_1;
package Package_2 is

   type Instance is tagged null record;
   subtype Class is Instance'Class;
   type Handle is access all Class;

end Package_2;
with T.Package_1;
with Package_2;

generic
   Max_Fred : in Fred := Fred'Last;
package T.Package_1.Classwide_Allocator is

   type Descriptor is record
      Field_1 : T.Package_1.Handle;
      Field_2 : Package_2.Handle;
   end record;

   function Get (Package_1 : in T.Package_1.Class;
                 F2 : in Package_2.Class
                ) return Descriptor;

end T.Package_1.Classwide_Allocator;
package body T.Package_1.Classwide_Allocator is

   function Get (Package_1 : in T.Package_1.Class;
                 F2 : in Package_2.Class
                ) return Descriptor is
   begin
      return (Field_1 => new T.Package_1.Class'(Package_1),
              Field_2 => new Package_2.Class'(F2)
              );
   end Get;

end T.Package_1.Classwide_Allocator;

with T.Package_1;
with Package_2;
with T.Package_1.Classwide_Allocator;

procedure Test is
   package P1 is new T.Package_1 (Integer);
   package Allocator is new P1.Classwide_Allocator;

   Field_1 : P1.Instance;
   Field_2 : Package_2.Instance;
   Descriptor : Allocator.Descriptor;
begin
   Descriptor := Allocator.Get (Field_1, Field_2);
end Test;
----

Compiling this with gnat 3.12p now gets the same results I get in my actual code,
namely:

gcc -c -Ic:/Development/Classwide_Allocator/ -I./ -g -gnatq -I-
c:/Development/Classwide_Allocator/test.adb

raised TYPES.UNRECOVERABLE_ERROR : comperr.adb:88
gnatmake: "c:/Development/Classwide_Allocator/test.adb" compilation error

Compilation exited abnormally with code 4 at Tue Dec 28 11:57:59


I'll forwarding this message along to report@gnat.com


--
T.E.D.

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