indirect_iterator_ref.rst

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.. Copyright David Abrahams 2006. Distributed under the Boost
.. Software License, Version 1.0. (See accompanying
.. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

::

  template <
      class Iterator
    , class Value = use_default
    , class CategoryOrTraversal = use_default
    , class Reference = use_default
    , class Difference = use_default
  >
  class indirect_iterator
  {
   public:
      typedef /* see below */ value_type;
      typedef /* see below */ reference;
      typedef /* see below */ pointer;
      typedef /* see below */ difference_type;
      typedef /* see below */ iterator_category;

      indirect_iterator();
      indirect_iterator(Iterator x);

      template <
          class Iterator2, class Value2, class Category2
        , class Reference2, class Difference2
      >
      indirect_iterator(
          indirect_iterator<
               Iterator2, Value2, Category2, Reference2, Difference2
          > const& y
        , typename enable_if_convertible<Iterator2, Iterator>::type* = 0 // exposition
      );

      Iterator const& base() const;
      reference operator*() const;
      indirect_iterator& operator++();
      indirect_iterator& operator--();
  private:
     Iterator m_iterator; // exposition
  };


The member types of ``indirect_iterator`` are defined according to
the following pseudo-code, where ``V`` is
``iterator_traits<Iterator>::value_type``

.. parsed-literal::

  if (Value is use_default) then
      typedef remove_const<pointee<V>::type>::type value_type;
  else
      typedef remove_const<Value>::type value_type;

  if (Reference is use_default) then
      if (Value is use_default) then
          typedef indirect_reference<V>::type reference;
      else
          typedef Value& reference;
  else
      typedef Reference reference;

  if (Value is use_default) then 
      typedef pointee<V>::type\* pointer;
  else 
      typedef Value\* pointer;

  if (Difference is use_default)
      typedef iterator_traits<Iterator>::difference_type difference_type;
  else
      typedef Difference difference_type;

  if (CategoryOrTraversal is use_default)
      typedef *iterator-category* (
          iterator_traversal<Iterator>::type,``reference``,``value_type``
      ) iterator_category;
  else
      typedef *iterator-category* (
          CategoryOrTraversal,``reference``,``value_type``
      ) iterator_category;


``indirect_iterator`` requirements
..................................

The expression ``*v``, where ``v`` is an object of
``iterator_traits<Iterator>::value_type``, shall be valid
expression and convertible to ``reference``.  ``Iterator`` shall
model the traversal concept indicated by ``iterator_category``.
``Value``, ``Reference``, and ``Difference`` shall be chosen so
that ``value_type``, ``reference``, and ``difference_type`` meet
the requirements indicated by ``iterator_category``.

[Note: there are further requirements on the
``iterator_traits<Iterator>::value_type`` if the ``Value``
parameter is not ``use_default``, as implied by the algorithm for
deducing the default for the ``value_type`` member.]

``indirect_iterator`` models
............................

In addition to the concepts indicated by ``iterator_category``
and by ``iterator_traversal<indirect_iterator>::type``, a
specialization of ``indirect_iterator`` models the following
concepts, Where ``v`` is an object of
``iterator_traits<Iterator>::value_type``:

  * Readable Iterator if ``reference(*v)`` is convertible to
    ``value_type``.
   
  * Writable Iterator if ``reference(*v) = t`` is a valid
    expression (where ``t`` is an object of type
    ``indirect_iterator::value_type``)

  * Lvalue Iterator if ``reference`` is a reference type.

``indirect_iterator<X,V1,C1,R1,D1>`` is interoperable with
``indirect_iterator<Y,V2,C2,R2,D2>`` if and only if ``X`` is
interoperable with ``Y``.


``indirect_iterator`` operations
................................

In addition to the operations required by the concepts described
above, specializations of ``indirect_iterator`` provide the
following operations.


``indirect_iterator();``

:Requires: ``Iterator`` must be Default Constructible.
:Effects: Constructs an instance of ``indirect_iterator`` with 
   a default-constructed ``m_iterator``.


``indirect_iterator(Iterator x);``

:Effects: Constructs an instance of ``indirect_iterator`` with
    ``m_iterator`` copy constructed from ``x``.

::

  template <
      class Iterator2, class Value2, unsigned Access, class Traversal
    , class Reference2, class Difference2
  >
  indirect_iterator(
      indirect_iterator<
           Iterator2, Value2, Access, Traversal, Reference2, Difference2
      > const& y
    , typename enable_if_convertible<Iterator2, Iterator>::type* = 0 // exposition
  );

:Requires: ``Iterator2`` is implicitly convertible to ``Iterator``.
:Effects: Constructs an instance of ``indirect_iterator`` whose 
    ``m_iterator`` subobject is constructed from ``y.base()``.


``Iterator const& base() const;``

:Returns: ``m_iterator``


``reference operator*() const;``

:Returns:  ``**m_iterator``


``indirect_iterator& operator++();``

:Effects: ``++m_iterator``
:Returns: ``*this``


``indirect_iterator& operator--();``

:Effects: ``--m_iterator``
:Returns: ``*this``