[depr.iterator]

The header <iterator> 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; }; }

The iterator template may be used as a base class to ease the definition of required types for new iterators.

[Note 1:

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]

[Example 1:

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]