Re: Access idiom

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Gene <gene.ressler@gmail.com> writes:

> In concept, what I'd need to do is something like this:
>
> type Node_Ptr_Type is access Node_Type'Class;
>
> procedure Op(P : in Threat_Type; Result : out Node_Ptr_Type) is
> begin
>    Result := P'Access; -- identity operation
> end Op;

I'm not sure exactly what you're trying to do,
but the following might be what you want:

  type Node_Ptr_Type is access constant Node_Type'Class;
                               ^^^^^^^^

  procedure Op(P : in Threat_Type; Result : out Node_Ptr_Type) is
  begin
     Result := P'Unchecked_Access; -- identity operation
                 ^^^^^^^^^^
  end Op;

or:

  type Node_Ptr_Type is access all Node_Type'Class;
                               ^^^

  procedure Op(P : in out Threat_Type; Result : out Node_Ptr_Type) is
                      ^^^
  begin
     Result := P'Unchecked_Access; -- identity operation
                 ^^^^^^^^^^
  end Op;

'Unchecked_Access can lead to dangling pointers -- you need to make sure
you don't pass nested objects to Op.

- Bob