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Subject: Re: Passing indefinite types
From: sbelmont700@gmail.com
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Date: 2013-02-05T13:16:10-08:00
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I had pretty much resigned myself to using the heap anyhow, this was mostly=
 just out of curiosity as to whether it could be done or not.  It seems a s=
hame that it cannot, since there are already mechanisms to safely pass loca=
l access values to longer-lived subprograms, so long as their are by themse=
lves or within records.  An array seems like the logical next step.

But in the interests of proving it can actually be done, here is my best ta=
ke on it: a (completly unreadable) linked list of access-discriminanted rec=
ords, where the callee would presumably iterate through them as needed.  Th=
is would work for limited types, too, whereas (most of?) the normal contain=
ers would not.


package k is

   type String_Holder (s : not null access string) is null record;
  =20
   type Node;
   type Node_Holder (n : not null access Node) is null record;

   type Node (string_data : not null access String_Holder;
              next_node   : access Node_Holder) is null record;
             =20
   function find (pattern : string;
                  sources : Node) return boolean;
                  =20
end k;

procedure p is

  s1   : aliased string :=3D "One thing";
  s2   : aliased string :=3D "another thing";
  s3   : aliased string :=3D "third thing";
 =20
  s1_h : aliased k.string_holder :=3D (s =3D> s1'access);
  s2_h : aliased k.string_holder :=3D (s =3D> s2'access);
  s3_h : aliased k.string_holder :=3D (s =3D> s3'access);

  n3   : aliased k.node :=3D (s3_h'access, null);
  n3_h : aliased k.node_holder :=3D (n =3D> n3'access);
 =20
  n2   : aliased k.node :=3D (s2_h'access, n3_h'access);
  n2_h : aliased k.node_holder :=3D (n =3D> n2'access);
 =20
  n1   : k.node :=3D (s1_h'access, n2_h'access);
 =20
  x : boolean :=3D k.find ("look ma, no heap!", n1);

begin
  null;
end;

Thanks again to everyone for their suggestions.

-sb