Constness in iterator_facade::operator->

[ras52]

The C++ standard states (table 72) that for an input
iterator, a->m is equivalent to (*a).m.  If operator*
returns a value_type by non-const value, it is possible
to call a non-const member function on the temporary
returned from the function.  However, the
operator_arrow_proxy class acts as a proxy to T const*
rather than T*, this that you can do

  (*i).non_const_method();

but not

  i->non_const_method();

for certain input iterators.


See discussion here:

http://lists.boost.org/Archives/boost/2006/07/107713.php
http://lists.boost.org/Archives/boost/2006/07/107740.php
http://lists.boost.org/Archives/boost/2006/07/107756.php