+public:
+ // Iterators
+ class const_iterator : public std::iterator<std::random_access_iterator_tag, ex, ptrdiff_t, const ex *, const ex &>
+ {
+ friend class ex;
+
+ public:
+ const_iterator() {}
+ const_iterator(const basic *bp_, size_t i_) : bp(bp_), i(i_) {}
+
+ bool operator==(const const_iterator &other) const
+ {
+ return bp == other.bp && i == other.i;
+ }
+
+ bool operator!=(const const_iterator &other) const
+ {
+ return !(*this == other);
+ }
+
+ bool operator<(const const_iterator &other) const
+ {
+ return i < other.i;
+ }
+
+ bool operator>(const const_iterator &other) const
+ {
+ return other < *this;
+ }
+
+ bool operator<=(const const_iterator &other) const
+ {
+ return !(other < *this);
+ }
+
+ bool operator>=(const const_iterator &other) const
+ {
+ return !(*this < other);
+ }
+
+ // This should return an ex&, but that would be a reference to a
+ // temporary value
+ ex operator*() const
+ {
+ return bp->op(i);
+ }
+
+#if 0
+ // How do we make this work in the context of the "reference to
+ // temporary" problem? Return an auto_ptr?
+ pointer operator->() const
+ {
+ return &(operator*());
+ }
+#endif
+
+ const_iterator &operator++()
+ {
+ ++i;
+ return *this;
+ }
+
+ const_iterator operator++(int)
+ {
+ const_iterator tmp = *this;
+ ++i;
+ return tmp;
+ }
+
+ const_iterator &operator+=(difference_type n)
+ {
+ i += n;
+ return *this;
+ }
+
+ const_iterator operator+(difference_type n) const
+ {
+ return const_iterator(bp, i + n);
+ }
+
+ inline friend const_iterator operator+(difference_type n, const const_iterator &it)
+ {
+ return const_iterator(it.bp, it.i + n);
+ }
+
+ const_iterator &operator--()
+ {
+ --i;
+ return *this;
+ }
+
+ const_iterator operator--(int)
+ {
+ const_iterator tmp = *this;
+ --i;
+ return tmp;
+ }
+
+ const_iterator &operator-=(difference_type n)
+ {
+ i -= n;
+ return *this;
+ }
+
+ const_iterator operator-(difference_type n) const
+ {
+ return const_iterator(bp, i - n);
+ }
+
+ inline friend difference_type operator-(const const_iterator &lhs, const const_iterator &rhs)
+ {
+ return lhs.i - rhs.i;
+ }
+
+ reference operator[](difference_type n) const
+ {
+ }
+
+ protected:
+ const basic *bp;
+ size_t i;
+ };
+
+ const_iterator begin() const { return const_iterator(get_pointer(bp), 0); }
+ const_iterator end() const { return const_iterator(get_pointer(bp), bp->nops()); }
+
+#if 0
+ // This doesn't work because of the "reference to temporary" problem
+ // in operator*()
+ typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
+ const_reverse_iterator rbegin() const { return const_reverse_iterator(end()); }
+ const_reverse_iterator rend() const { return const_reverse_iterator(begin()); }
+#endif
+