[depr.iterator]

# Annex D (normative) Compatibility features [[depr]](./#depr)

## D.17 Deprecated iterator class template [depr.iterator]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/future.tex#L638)

The header [<iterator>](iterator.synopsis#header:%3citerator%3e "24.2 Header <iterator>&nbsp;synopsis [iterator.synopsis]") has the following addition:

[🔗](#lib:iterator)

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](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/future.tex#L655)

Theiterator template may be used as a base class to ease the definition of required types
for new iterators[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/future.tex#L661)

[*Note [1](#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[.](#3.sentence-1)

— *end note*]

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/future.tex#L668)

[*Example [1](#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*]