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From: Natasha Kerensikova <lithiumcat@instinctive.eu>
Newsgroups: comp.lang.ada
Subject: Are limited interfaces deeper than non-limited ones?
Date: Sun, 9 Apr 2017 20:52:28 -0000 (UTC)
Organization: A noiseless patient Spider
Message-ID: <slrnoel7u4.1m1.lithiumcat@nat.rebma.instinctive.eu>
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Date: 2017-04-09T20:52:28+00:00
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Hello,

I know that accessibility levels come with a host of problems, but I
thought that static accessibility was reasonably well understood, and
yet I encounter this very strage situation. Everything else being
otherwise equal, everything works fine with a non-limited interface, but
GNAT FSF v6.3.1 rejects the limited interface.

Is there something wrong with my GNAT or is there really something I
miss going on here?

Thanks in advance for your help,
Natasha


----- mini.ads ------
generic
   type Held_Data (<>) is limited private;
package Mini is

   type Holder is private;

   function Create
     (Constructor : not null access function return Held_Data)
     return Holder;

private

   type Data_Access is access Held_Data;

   type Holder is record
      Ref : Data_Access;
   end record;

end Mini;
----- mini.adb ------
package body Mini is

   function Create
     (Constructor : not null access function return Held_Data)
     return Holder is
   begin
      return (Ref => new Held_Data'(Constructor.all));
   end Create;

end Mini;
----- non_lim.ads ------
with Mini;

package Non_Lim is

   type Data is interface;

   package Instance is new Mini (Data'Class);

end Non_Lim;
----- lim.ads ------
with Mini;

package Lim is

   type Data is limited interface;

   package Instance is new Mini (Data'Class);

end Lim;

----- GNAT output ------
$ gnatmake non_lim.ads
ada -c non_lim.ads
ada -c mini.adb
$ gnatmake lim.ads
ada -c lim.ads
lim.ads:7:04: warning: in instantiation at mini.adb:7
lim.ads:7:04: warning: accessibility check failure
lim.ads:7:04: warning: "Program_Error" will be raised at run time