[fpc-pascal] Clone a instance of object

[Mattias Gaertner]

On Mon, 23 Sep 2013 11:46:54 +0200 (CEST)
Michael Van Canneyt <michael at freepascal.org> wrote:

> 
> 
> On Mon, 23 Sep 2013, Zaher Dirkey wrote:
> 
> > 
> > On Mon, Sep 23, 2013 at 10:02 AM, Michael Van Canneyt <michael at freepascal.org> wrote:
> >       Var
> >         C : TBaseObjectClass;
> >       begin
> >         C:=TBaseObjectClass(ClassType);
> >         Result:=C.Create;
> >       end;
> > 
> > 
> > ​Yes, that help me, thanks.
> > 
> > Now about assigning I must repeat it (assign) for every child class copy its field members, is there any trick to copy the values like assigning record var to another record
> > var?
> > I know it is kind of strange way :P
> 
> There is no such safe mechanism.

Well, actually there is a safe mechanism. You use a record to store the
class variables. But it looks clumsily:

type
 TMyClass = class(TPersistent)
 private
   type
     TMyClassVars = record
       a,b,c: string;
     end;
 private
   F: TMyClassVars;
 public
   procedure Assign(Source: TPersistent);
   property a: string read F.a write F.a;
 end;

procedure TMyClass.Assign(Source: TPersistent);
begin
  F:=TMyClass(Source).F;
  inherited;
end;

 
> The best you can do is make the properties published, and write an RTTI lookup routine that copies all Published values.
> I've done this several times, it works well for most situations.

Mattias