Re: Cloning a Class Wide Data Type with "new"?

["David C. Hoos" <david.c.hoos.sr@ada95.com>]

"Warren W. Gay VE3WWG" <ve3wwg@cogeco.ca> wrote in message
news:3EE097D5.2010901@cogeco.ca...
> I havn't had much time to research this one yet, but I've
> got stuck trying to clone a class wide type this morning,
> on my way to work. A sample program is provided below.
>
> 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 is a sample program that distills the problem:
>
>
> 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'(Orig);

The operand of the qualified expression must first be converted to the
Base_Class -- i.e.:
    Cloned : Base_Access := new Base_Class'(Base_Class (Orig));

See RM95 4.7 (3)

> begin
>
>     Put_Line("Cloned.V = " & Cloned.V'Img);
>
> end TProg;
>
>
> TIA, Warren.
> -- 
> Warren W. Gay VE3WWG
> http://home.cogeco.ca/~ve3wwg
>
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