"Gennadiy Rozental" <gennadiy.rozental@thomson.com> writes:
"Neal Becker" <ndbecker2@verizon.net> wrote in message news:c7uljb$etk$1@sea.gmane.org...
In iterator_facade.hpp:
reference operator*() const
Why the const?
So you could dereference const iterators
I suppose we could provide a non-const overload, but that doesn't sound like the right tool for this particular job.
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.
Make'em mutable. Dereference is 'naturally' const operation. So special cases should be marked as special.
I think that's the right thing to do, but not quite the right explanation. The reason to make the function object mutable is that changes to the function object don't affect the "logical constness" of the iterator. Any state in the function object only changes "once per position" when it's embedded in the iterator, so that operator++ is the effectively non-const operation. The following input iterator requirements guarantee that operator* isn't allowed to advance the iterator: expression type semantics,pre/post-conditions ---------- ---- ----------------------------- *a convertible to T pre: a is dereferenceable. If a==b and (a,b) is in the domain of == then *a is equivalent to *b. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com