Re: class containing a list of itself

From: Rob Williscroft (rtw_at_freenet.co.uk)
Date: 08/25/04 

Date: 25 Aug 2004 14:34:22 GMT

Sharad Kala wrote in news:2p3lcbFfv27rU1@uni-berlin.de in comp.lang.c++:

>> But your code will
>> be non-standard until/unless the standard gets changed.

With hindsight I should have possibly been clearer that the requirment
for completeness of argument types, is only for instantiation *not*
for declaration:

#include <list>

struct X;

extern std::list< X > xlist;

struct X {};

std::list< X > xlist;

>
> I think Standard does mention about this in Section 14.3.1/2
> " ...[Note: a template type argument may be an incomplete type. ] "
>

14.3.1 == Templates / Template type arguments.

Not really relevent to wether or not std::list< T > can take
an incomplete T and be instantiated *before* T is complete.

IOW: you can always (*) declare a specialization which has an incomplete
argument type, what is dependant on the template defenition is wether
you can instantiate such a specialization.

*) Unless such a declaration requires instantition of an
   un-instantiatable specialization:

   template < typename > struct empty {};

   template < typename T, typename U = typename empty< T >::type >
   struct no
   {
   };

   extern no< int > nope;

Rob. 

-- 
http://www.victim-prime.dsl.pipex.com/

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