🚀 go-pugleaf

gilem@rpi.edu (Michael R. Gile) writes:
	...
>is there any way to use the typeinfo which is returned from typeid
>to create a new object of that type?  I have been looking at the
>draft, and this doesn't seem to be possible.  The reason that I ask
>is that it is very useful when you have a container full of things
>to be able to duplicate the container.  If all of the objects

Actually, this specific task seems to call for a virtual clone()
function, one which copies a *specific* object (the canonical
form for it is I guess "return new T(*this);" for any T); if
typeinfo were to include a "factory method", it surely would
NOT also carry around all the instance-data needed for this
anyway, in other terms it would at most obviate the need for
a virtual make() (canonical form "return new T();"), which
has its place but is of much rarer occurrence than clone().

>are not of the same type (maybe they are derived classes), then 
>it is not easy to duplicate each object.  Currently, my code gets
>around this by making a virtual function for each object that needs
>to duplicate itself, but I was hoping that there would be a standard
>way to do this now that we have RTTI.  Am I the only one who thinks
>that this feature would be incredibly useful?

Oh, no, the "exemplar idiom", as e.g. Coplien calls it, is indeed
quite often used; but the clone() form of it is the most
frequent, having to do more with a specific object than
with just its _type_ -- and the amount of boilerplate to
write for it, though non-null, is not huge either...

Perhaps some template magic could help...?


Alex
--
DISCLAIMER: these are TOTALLY personal opinions and viewpoints, NOT connected
in any way with my employer, nor any other organization or individual!
Email: martelli@cadlab.it                            Phone: +39 (51) 597313
CAD.LAB s.p.a., v. Ronzani 7/29, Casalecchio, Italia   Fax: +39 (51) 597120

[ comp.std.c++ is moderated.  Submission address: std-c++@ncar.ucar.edu.
  Contact address: std-c++-request@ncar.ucar.edu.  The moderation policy
  is summarized in http://dogbert.lbl.gov/~matt/std-c++/policy.html. ]