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Date: Sat, 09 Feb 2008 15:57:22 -0500
From: "Peter C. Chapin" <pchapin@sover.net>
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Subject: Another question about controlled types.
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Date: 2008-02-09T15:57:22-05:00
List-Id: <comp.lang.ada>

I'm using GNAT GPL 2007. I understand that Ada 2005 allows one to return 
limited types from functions. Consider the following package 
specification and body:

package Check is
    type Some_Type is limited private;
    function Make(I : Integer) return Some_Type;
private
    type Some_Type is
       record
          Component : Integer;
       end record;
end Check;

package body Check is
    function Make(I : Integer) return Some_Type is
       Result : Some_Type;
    begin
       Result.Component := I;
       return Result;
    end Make;
end Check;

In fact, this compiles fine using "gnatmake -gnatc check.adb"

Now consider the following slight (but significant!) change to the 
specification:

with Ada.Finalization;

package Check is
    type Some_Type is limited private;
    function Make(I : Integer) return Some_Type;
private
    type Some_Type is new Ada.Finalization.Limited_Controlled with
       record
          Component : Integer;
       end record;
end Check;

In this case the full view of Some_Type is controlled. Now when I 
attempt to compile the package I get:

check.adb:8:14: (Ada 2005) cannot copy object of a limited type (RM-2005 
6.5(5.5/2))
check.adb:8:14: return by reference not permitted in Ada 2005
check.adb:8:14: consider switching to return of access type

I'm not sure why there is a problem now. I tried declaring Some_Type as 
tagged in the visible part of the package but that didn't help.

Peter