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From: "Rego, P." <pvrego@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Constructors with multiple inheritance
Date: Tue, 8 Nov 2011 18:24:53 -0800 (PST)
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Date: 2011-11-08T18:24:53-08:00
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>    function Construct (Object_Reference : access Parent_Class)
>       return Parent_Class_Ptr;

I tried this approach in the following code, but it still complains about the null object. 

    -- test_pkg.ads
    package Test_Pkg is
       type Test_Class is tagged;
       type Test_Class_Ptr is access all Test_Class;

       function Construct (T : access Test_Class) return Test_Class_Ptr;

       task type Primary_Task (This : not null access Test_Class);

       type Test_Class is tagged limited
          record
             Info    : Integer := 0;
             Value   : Float;
             Primary : Primary_Task (Test_Class'Access);
          end record;
    end Test_Pkg;

    -- test_pkg.adb
    with Text_IO; use Text_IO;
    package body Test_Pkg is
       task body Primary_Task is
       begin
          loop
             Put_Line (Integer'Image (This.Info) & "__");
             delay 0.2;
          end loop;
       end Primary_Task;

       function Construct (T : access Test_Class) return Test_Class_Ptr is
          T_Ptr : constant Test_Class_Ptr := new Test_Class;
       begin
          T_Ptr.Info := T.Info + 1;
          T_Ptr.Value := 0.0;
          return T_Ptr;
       end Construct;
    end Test_Pkg;

    -- test_pkg_user.adb
    with Test_Pkg;
    with Text_IO; use Text_IO;

    procedure Test_Pkg_User is
       Test_Obj : Test_Pkg.Test_Class_Ptr;
    begin
       Test_Obj := Test_Obj.Construct;
       Put_Line ("Value = "&Integer'Image (Test_Obj.Info));
    end Test_Pkg_User;

The message I get is the following:
    c:\tst>gnatmake test_pkg_user.adb
    gcc -c test_pkg_rev623_user.adb
    test_pkg_user.adb:12:16: warning: null value not allowed here
    test_pkg_user.adb:12:16: warning: "Constraint_Error" will be raised at run time
    gcc -c test_pkg.adb
    gnatbind -x test_pkg_user.ali
    gnatlink test_pkg_user.ali

What am I still doing wrong? Thanks again.

Note: Sure if I put in test_pkg_user.adb
    Test_Obj : Test_Pkg.Test_Class_Ptr := new Test_Pkg.Test_Class; 
it returns me a build with no warning, but I think this way I allocate memory twice to the pointer (one in the call new Test_Pkg.Test_Class and the other in the construct method execution), right?