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From: mcq95@earthlink.net (Marc A. Criley)
Newsgroups: comp.lang.ada
Subject: Re: Cloning a Class Wide Data Type with "new"?
Date: 6 Jun 2003 11:18:33 -0700
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"Warren W. Gay VE3WWG" <ve3wwg@cogeco.ca> wrote in message news:<3EE097D5.2010901@cogeco.ca>...
> I need to be able to allocate and then copy an arbitrary
> tagged type (based upon a base type) into the newly
> allocated object. There's gotta be a way to do this..
> I just can't remember it!
> 
> The problem is the operation of the form of :
> 
>    Cloned : Base_Access := new Base_Class'(Orig);

Here's what I did to get it to compile...

     Cloned : Base_Access := new Base_Class'Class'(Base_Class(Orig));

...AND it seemed to work--though it'd be a little iffy for me to
explain in detail what's going on.

Marc A. Criley

Modified sample program follows:

with Ada.Text_IO;
use Ada.Text_IO;

procedure TProg is

    type Base_Type is tagged
       record
          V :      Integer;
       end record;

    type Base_Access is access all Base_Type'Class;
    subtype Base_Class is Base_Type'Class;

    type Derived_Type is new Base_Type with
       record
          Z :      Natural;
       end record;

    -- This is the original object to be cloned
    Orig :   Derived_Type := ( V => 32, Z => 99 );

    -- This is a local copy (easy)
    Copied : Base_Class  := Orig;

    -- Allocate Cloned to be same as Orig (the problem)
    Cloned : Base_Access := new Base_Class'Class'(Base_Class(Orig));
begin

    Put_Line("Cloned.V = " & Cloned.V'Img);
    Put_Line("Cloned.Z = " & Derived_Type(Cloned.all).Z'Img);

end TProg;