mockingbirdnest · Mar 15, 2017
diff --git a/‎base/container_iterator.hpp
+2 b/‎base/container_iterator.hpp
+2
diff --git a/‎base/container_iterator_body.hpp
+8-3 b/‎base/container_iterator_body.hpp
+8-3
@@ -21,6 +21,8 @@ class IteratorOn final {
 
   Iterator const& iterator() const;
 
+  std::int64_t distance_from_begin() const;
+
  private:
   not_null<Container*> container_;
   Iterator iterator_;
 
@@ -12,15 +12,20 @@ IteratorOn<Container>::IteratorOn(not_null<Container*> container,
     : container_(container),
       iterator_(iterator) {}
 
+template<typename Container>
+template<typename>
+IteratorOn<Container> IteratorOn<Container>::Erase() const {
+  return IteratorOn(container_, container_->erase(iterator_));
+}
+
 template<typename Container>
 typename Container::iterator const& IteratorOn<Container>::iterator() const {
   return iterator_;
 }
 
 template<typename Container>
-template<typename>
-IteratorOn<Container> IteratorOn<Container>::Erase() const {
-  return IteratorOn(container_, container_->erase(iterator_));
+std::int64_t IteratorOn<Container>::distance_from_begin() const {
+  return std::distance(container_->begin(), iterator_);
 }
 
 }  // namespace base