[boost] [iterator facade] Why is dereference const?

From: Neal Becker (ndbecker2_at_[hidden])
Date: 2004-05-12 21:12:59

In iterator_facade.hpp:

      reference operator*() const

Why the const?  I am writing function_input_iterator (again), using
iterator_facade.  The functor used as a generator may not be const - it
might well have state.  Therefore, dereference changes the state, and so
isn't const.