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From: Maciej Sobczak <see.my.homepage@gmail.com>
Newsgroups: comp.lang.ada
Subject: Dynamic allocation of unconstrained types
Date: Wed, 30 Sep 2009 07:29:26 -0700 (PDT)
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Consider:

procedure Test is

   package P is
      type T (<>) is limited private;
      function Create return T;
   private
      type T is limited record
         I : Integer;
      end record;
   end P;

   package body P is
      function Create return T is
      begin
         return T'(I => 123);
      end Create;
   end P;

   S : access P.T;

begin
   S := new P.T'(P.Create);   -- ??? (this is line 22)
end Test;

GNAT says:

test.adb:22:19: uninitialized unconstrained allocation not allowed
test.adb:22:19: qualified expression required

Interestingly, it works with Strings.
Why doesn't GNAT recognize it as a qualified expression?

I would like to allocate dynamically something that has a constructor
function. There is no other way to create the object than with that
function and presumably it should be possible to use it with dynamic
allocation.
How can I do it?

BTW - when preparing this example I tried first with empty (null)
record, but got stuck with proper way to return an instance of T. I
remember there was some older discussion about it, but for some reason
I cannot find it and the following:

return T'(others => <>);

is rejected as well.
What is the proper way to create null aggregates?

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com

Database Access Library for Ada: www.inspirel.com/soci-ada