Input Iterators
- Specialized read_only forward iterator:
// comparison logic
bool operator == (const Iterator& ) const; // equality operator
bool operator != (const Iterator& ) const; // non-equality operator
// read-only element access (rvalue only)
const value_type& operator * () const; // dereference operator
// motion
Iterator& operator ++ (); // prefix increment
Iterator operator ++ (int); // postfix increment
// proper type
Iterator () // constructor
~Iterator () // destructor
Iterator (const Iterator& ); // copy constructor
// no assignment operator