On Thu, Feb 23, 2012 at 9:57 AM, Rob Desbois <rob.desbois@gmail.com> wrote:
I have the following iterator_adaptor type:
template< class NODE > struct node_iterator: public boost::iterator_adaptor< node_iterator<NODE>, // Derived NODE*, // Base typename NODE::value_type // Value > { typename NODE::value_type dereference() const { return this->base_reference()->data(); } };
// and later: typedef detail::node_iterator<node_type> iterator; typedef detail::node_iterator<const node_type> const_iterator;
This throws up the issue that in const_iterator, Value is not const, producing the following error: /usr/include/boost/iterator/iterator_facade.hpp:517:32: error: invalid initialization of non-const reference of type ‘container::detail::node_iterator<const container::detail::node<long unsigned int> >::reference {aka long unsigned int&}’ from an rvalue of type ‘container::detail::node<long unsigned int>::value_type {aka long unsigned int}’
I could do some type traits magic with is_same, is_const and add_const to add the constness to Value if present on NODE, but is this the right way to do it? I've also thought about indirect_iterator - but adding operator*() to the node type seems not quite right. Perhaps transform_iterator...or is there some different method that might be more suitable?
I favoured the type traits magic approach, and publish the resulting value type as the value type of the iterator... typedef typename if_<is_const<NODE>, const typename NODE::value_type, typename NODE::value_type>::type value_type; - Rob (J)