Raoul Gough <yg-boost-users@m.gmane.org> writes:
David Abrahams <dave@boost-consulting.com> writes:
Raoul Gough <yg-boost-users@m.gmane.org> writes:
Using gcc 3.2 (on MinGW) the template parameter defaults for indirect_iterator_generator don't work with shared_ptr. This has been discussed* on the list before, but there doesn't seem to have been a user-friendly resolution to the issues involved (at least not in release 1_30_0).
Right. The user-friendly solution is to use the iterator adaptors in the current Boost CVS. There won't be a fix for 1.30.0.
Hi Dave,
Thanks very much for your reply. I've switched to the CVS head, and can get my test case to compile as follows:
#include <boost/iterator/indirect_iterator.hpp> #include <boost/shared_ptr.hpp> #include <list>
int main () { typedef std::list<boost::shared_ptr<int> > ListType; typedef ListType::iterator BaseIterator; typedef boost::indirect_iterator<BaseIterator> Adapter; }
Is that about right?
Yep.
It looks like the main documentation isn't up to date yet, since it links to libs/utility/indirect_iterator.htm which still talks about indirect_iterator_generator.
Right.
On a different note, /libs/iterator/doc/facade-and-adaptor.html says:
If the default is used for Value, then there must be a valid specialization of iterator_traits for the value type of the base iterator.
That's not quite accurate. The actual rule is: if the value_type of the Base iterator is a class with a nested ::element_type, remove_const< iterator_traits<Base>::value_type::element_type
::type
will be the value type of the resulting iterator. Otherwise, there must be a valid iterator_traits specialization of iterator_traits for the value type of the base iterator. We probably ought to define a public referent<T> metafunction in namespace boost which implements that logic, so that people can specialize it.
Is a full iterator_traits actually necessary? Just seems to me that there is conceptual difference between (let's say) dereferencable_traits (which any proxy type could have) and a full-blown iterator_traits (which smart pointers probably wouldn't have).
Right. -- Dave Abrahams Boost Consulting www.boost-consulting.com