Member Function Iterator Adaptor

I'm trying to build a member function iterator adaptor. (Maybe there already is one and I'm not finding it?) This would be an iterator adaptor where the adaptor returns the result of calling a member function of the base iterator. I think this is a pretty straightforward iterator adaptor. What I am missing is the ability to work out the value_type of the iterator. This would be the return type of the member function being used. I thought I could use boost::call_traits< MemberFunction >::value_type, but that returns the entire type of the member function. I think call_traits<> is not what I am looking for. Pointers or suggests would be greatly welcomed. Thanks! ...Duane