Annex D (normative) Compatibility features [depr]

D.16 Deprecated iterator primitives [depr.iterator.primitives]

D.16.1 Basic iterator [depr.iterator.basic]

1
#
The header <iterator> ([iterator.synopsis]) has the following addition: 
namespace std {
  template<class Category, class T, class Distance = ptrdiff_t,
           class Pointer = T*, class Reference = T&>
  struct iterator {
    using iterator_category = Category;
    using value_type        = T;
    using difference_type   = Distance;
    using pointer           = Pointer;
    using reference         = Reference;
  };
}
2
#
The iterator template may be used as a base class to ease the definition of required types for new iterators.
3
#
[Note
:
If the new iterator type is a class template, then these aliases will not be visible from within the iterator class's template definition, but only to callers of that class.
— end note
]
4
#
[Example
:
If a C++ program wants to define a bidirectional iterator for some data structure containing double and such that it works on a large memory model of the implementation, it can do so with: 
class MyIterator :
  public iterator<bidirectional_iterator_tag, double, long, T*, T&> {
  // code implementing ++, etc.
};
— end example
]