Consider a container such as
std::vector > my_container;
I want to be able to iterate over the ints of this container so, following
the tutorial to the iterator_adaptor docs, came up with
template <typename BaseIterator>
class first_iter
: public boost::iterator_adaptor<
first_iter<BaseIterator>,
BaseIterator,
boost::use_default,
boost::use_default,
typename BaseIterator::value_type::first_type &
>
{
// snip body
};
This works fine so long as BaseIterator::value_type is not const, but falls
over when it is because I've defined the 'super_t::reference' type to be
mutable.
I guess that I need a piece of metafunction magic, but my naive
implementation fails
typename boost::mpl::apply_if<
boost::is_const<typename BaseIterator::value_type>
, typename BaseIterator::value_type::first_type const &
, typename BaseIterator::value_type::first_type &
>::type
trial.C:38: error: no type named `type' in `struct
boost::mpl::apply_if<
boost::is_const >,
const int&,
int&>'
I must admit I'm a bit baffled. There plainly is a 'type' in the apply_if
class template. Any pointers? I attach the code as I have it.
While I'm at it, is there not something in the MPL that will return the
appropriate const-qualified reference for me? None of the header file
names in boost/mpl jump out and grab me, but I may well be looking in the
wrong place.
Regards,
Angus
