Re: Asking for trouble with incomplete types?

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.language

Date:

Wed, 21 Feb 2007 18:49:08 -0500

Message-ID:

<uehFiLhVHHA.392@TK2MSFTNGP06.phx.gbl>

Ben Voigt <rbv@nospam.nospam> wrote:

"Igor Tandetnik" <itandetnik@mvps.org> wrote in message
news:uNv8UCgVHHA.4964@TK2MSFTNGP06.phx.gbl...

Mark Randall <markyr@gEEEEEmail.com> wrote:

I wish to have a class contain a list of itself

You can't, in general. You might get away with it with some
containers on some STL implementations, but it's non-portable. From
C++ standard: 17.4.3.6/2 In particular, the effects are undefined in
the following
cases:
...
- if an incomplete type (3.9) is used as a template argument when
instantiating a template component.

Couldn't Curiously Recurring Template Pattern be used to overcome
this?

I'm not sure what you have in mind. Could you demonstrate?

Usually "Curiously Recurring Template Pattern" means something like
this:

template <class T> class Base { ... };
class Derived : public Base<Derived> { ... };

Here, quite obviously, Base is designed to be instantiated on an
incomplete type. On the other hand, C++ standard library templates
explicitly must not be instantiated on an incomplete type. I don't quite
see how Curiously Recurring Template Pattern applies.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925