Re: [Boost-users] Problem with iterator_facade

17 Sep 2008

      Robert Dailey wrote:
...
Hi,
I have the following iterator_facade class:
class PassIterator
      : public boost::iterator_facade<
      	PassIterator,
      	Pass,
      	boost::forward_traversal_tag
      >
  {
  public:
      PassIterator();
PassIterator( Effect const& effect );
private:
      void increment();
      Pass& dereference() const;
Pass m_pass;
friend class boost::iterator_core_access;
  };
Note how my Pass object is stored by-value in my PassIterator class.
When I attempt to compile this class, it fails because dereference()
is const and it is trying to return a reference to a const member.
However, if I make dereference() non-const, it still fails because the
base class is calling into PassIterator::dereference() through a const
member function as well, so dereference() *must* be const in order to
be callable by boost.
How can I overcome this issue? const_cast? mutable? Thanks.
I guess you want:

class PassIterator
		: public boost::iterator_facade<
			PassIterator,
			const Pass, // #1
			boost::forward_traversal_tag
		>

...
                const Pass& dereference() const; // #2
...
};

Alternatively you could do this:

class PassIterator
		: public boost::iterator_facade<
			PassIterator,
			Pass, // #1
			boost::forward_traversal_tag,
                         Pass // #2
		>

...
                Pass dereference() const; // #3
...
};

Greetings from Bremen,

Daniel Krügler