Variadic templates and CRTP

[Alban Linard]

Hi,

either i do not understand some parts of variadic templates, or g++
has an erronous handling of types canonization when using variadic
templates and CRTP. Exemple code below.

/* g++-mp-4.5 (GCC) 4.5.0 20091001 (experimental)
 * g++-mp-4.5 -std=c++0x bug.cc
 * In function 'int main()':
 * 25:41: error: invalid initialization of reference of type 'base<a,
derived<a> >&' from expression of type 'derived<a>'
 * (hint: internal compiler error on some other uses, canonical types
differ for identical types, for 'base<a, derived<a> >')
 */

struct a {};

template < typename T, typename ENCLOSING >
struct base;

template < typename ENCLOSING >
struct base< a, ENCLOSING >
{};

template < typename... T >
struct derived
  : public base< T, derived< T... > >...
{};

int main()
{
  derived< a > instance;
  base< a, derived< a > >& a_instance = instance;
}

What have i done wrong or is it a bug ?
Thanks,
Alban Linard