Re: [Q] non-limited record and "self-pointer"

[Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>]

Stephen Leake <stephen_leake@acm.org> wrote:
: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de> writes:
: 
:> Stephen Leake <stephen_leake@acm.org> wrote:
:> : I'm not clear what you are asking. 
:> 
:> I'm puzzled too by the compiler's silence, because AFAIK a record cannot
:> silently become limited?
: 
: Post a complete, compilable example, and I'll take another look at it.

There it is, ObjectAda 7.2.2 does not complain either.


with sets;
package some_sets is new sets(Integer);

with some_sets;  use some_sets;
procedure simple_test is
   s1, s2: Read_Only_Set;
   s: Set;
   p: Set_Ptr;
begin
   s1 := s2;
   p := value_in_place(s);
end simple_test;



with Charles.Sets.Sorted.Unbounded;
generic
   type Element is private;

   with function "<"(L, R: Element) return Boolean is <>;
   with function "="(L, R: Element) return Boolean is <>;

   --with function wide_image(e: Element) return Wide_String is <>;
package Sets is



   type Read_Only_Set is tagged private;


   --  Modifiable Sets

   type Set is new Read_Only_Set with private;


   type Set_Ptr is access all Read_Only_Set'class;

   function value_in_place(container: Set) return Set_Ptr;
   --  a pointer to container (avoids copying)


private
   package Implementation is
      new Charles.Sets.Sorted.Unbounded(Element);

   type Read_Only_Set is tagged
      record
         container: Implementation.Container_Type;

         self: Set_Ptr := Read_Only_Set'unchecked_access;
         --  used in value_in_place

      end record;

   type Set is new Read_Only_Set with record
      frozen: Boolean := true;
   end record;


end Sets;



package body Sets is

   use Implementation;



   -- ----------------
   -- value_in_place
   -- ----------------
   --  every object of type Set points to itself

   function value_in_place(container: Set) return Set_Ptr is
      -- cont: aliased Set;
      -- for cont'address use container'address;
      -- cannot overlay controlled
      -- package set_ptrs is new System.Address_to_Access_conversions(Set);
   begin
      return container.self;
   end value_in_place;



end Sets;