18. The iterator abstraction

• Iterators are a widely used abstraction in the STL

• The idea is to have something that can be used with
  arrays, strings, lists, and even trees.

• Combined with liberal typedefing, it is possible to switch representations with a minimum of other changes:

  
      class Container {
          typedef std::vector< int > StorageType;
  
          typedef StorageType::const_iterator ConstStorageIter;
          typedef StorageType::iterator StorageIter;
  
          StorageType m_buffer;
          //...
      };