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.. 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)
.. Version 1.3 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG for TR1.
.. Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.
.. parsed-literal::
template <
class Derived
, class Value
, class CategoryOrTraversal
, class Reference = Value&
, class Difference = ptrdiff_t
>
class iterator_facade {
public:
typedef remove_const<Value>::type value_type;
typedef Reference reference;
typedef Value\* pointer;
typedef Difference difference_type;
typedef /* see below__ \*/ iterator_category;
reference operator\*() const;
/* see below__ \*/ operator->() const;
/* see below__ \*/ operator[](difference_type n) const;
Derived& operator++();
Derived operator++(int);
Derived& operator--();
Derived operator--(int);
Derived& operator+=(difference_type n);
Derived& operator-=(difference_type n);
Derived operator-(difference_type n) const;
protected:
typedef iterator_facade iterator_facade\_;
};
// Comparison operators
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type // exposition
operator ==(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator !=(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator <(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator <=(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator >(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator >=(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
// Iterator difference
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
/* see below__ \*/
operator-(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
// Iterator addition
template <class Dr, class V, class TC, class R, class D>
Derived operator+ (iterator_facade<Dr,V,TC,R,D> const&,
typename Derived::difference_type n);
template <class Dr, class V, class TC, class R, class D>
Derived operator+ (typename Derived::difference_type n,
iterator_facade<Dr,V,TC,R,D> const&);
__ `iterator category`_
__ `operator arrow`_
__ brackets_
__ minus_
.. _`iterator category`:
The ``iterator_category`` member of ``iterator_facade`` is
.. parsed-literal::
*iterator-category*\ (CategoryOrTraversal, reference, value_type)
where *iterator-category* is defined as follows:
.. include:: facade_iterator_category.rst
The ``enable_if_interoperable`` template used above is for exposition
purposes. The member operators should only be in an overload set
provided the derived types ``Dr1`` and ``Dr2`` are interoperable,
meaning that at least one of the types is convertible to the other. The
``enable_if_interoperable`` approach uses SFINAE to take the operators
out of the overload set when the types are not interoperable.
The operators should behave *as-if* ``enable_if_interoperable``
were defined to be::
template <bool, typename> enable_if_interoperable_impl
{};
template <typename T> enable_if_interoperable_impl<true,T>
{ typedef T type; };
template<typename Dr1, typename Dr2, typename T>
struct enable_if_interoperable
: enable_if_interoperable_impl<
is_convertible<Dr1,Dr2>::value || is_convertible<Dr2,Dr1>::value
, T
>
{};
``iterator_facade`` Requirements
--------------------------------
The following table describes the typical valid expressions on
``iterator_facade``\ 's ``Derived`` parameter, depending on the
iterator concept(s) it will model. The operations in the first
column must be made accessible to member functions of class
``iterator_core_access``. In addition,
``static_cast<Derived*>(iterator_facade*)`` shall be well-formed.
In the table below, ``F`` is ``iterator_facade<X,V,C,R,D>``, ``a`` is an
object of type ``X``, ``b`` and ``c`` are objects of type ``const X``,
``n`` is an object of ``F::difference_type``, ``y`` is a constant
object of a single pass iterator type interoperable with ``X``, and ``z``
is a constant object of a random access traversal iterator type
interoperable with ``X``.
.. _`core operations`:
.. topic:: ``iterator_facade`` Core Operations
+--------------------+----------------------+-------------------------+---------------------------+
|Expression |Return Type |Assertion/Note |Used to implement Iterator |
| | | |Concept(s) |
+====================+======================+=========================+===========================+
|``c.dereference()`` |``F::reference`` | |Readable Iterator, Writable|
| | | |Iterator |
+--------------------+----------------------+-------------------------+---------------------------+
|``c.equal(y)`` |convertible to bool |true iff ``c`` and ``y`` |Single Pass Iterator |
| | |refer to the same | |
| | |position. | |
+--------------------+----------------------+-------------------------+---------------------------+
|``a.increment()`` |unused | |Incrementable Iterator |
+--------------------+----------------------+-------------------------+---------------------------+
|``a.decrement()`` |unused | |Bidirectional Traversal |
| | | |Iterator |
+--------------------+----------------------+-------------------------+---------------------------+
|``a.advance(n)`` |unused | |Random Access Traversal |
| | | |Iterator |
+--------------------+----------------------+-------------------------+---------------------------+
|``c.distance_to(z)``|convertible to |equivalent to |Random Access Traversal |
| |``F::difference_type``|``distance(c, X(z))``. |Iterator |
+--------------------+----------------------+-------------------------+---------------------------+
``iterator_facade`` operations
------------------------------
The operations in this section are described in terms of operations on
the core interface of ``Derived`` which may be inaccessible
(i.e. private). The implementation should access these operations
through member functions of class ``iterator_core_access``.
``reference operator*() const;``
:Returns: ``static_cast<Derived const*>(this)->dereference()``
``operator->() const;`` (see below__)
__ `operator arrow`_
:Returns: If ``reference`` is a reference type, an object
of type ``pointer`` equal to::
&static_cast<Derived const*>(this)->dereference()
Otherwise returns an object of unspecified type such that,
``(*static_cast<Derived const*>(this))->m`` is equivalent to ``(w = **static_cast<Derived const*>(this),
w.m)`` for some temporary object ``w`` of type ``value_type``.
.. _brackets:
*unspecified* ``operator[](difference_type n) const;``
:Returns: an object convertible to ``value_type``. For constant
objects ``v`` of type ``value_type``, and ``n`` of type
``difference_type``, ``(*this)[n] = v`` is equivalent to
``*(*this + n) = v``, and ``static_cast<value_type
const&>((*this)[n])`` is equivalent to
``static_cast<value_type const&>(*(*this + n))``
``Derived& operator++();``
:Effects:
::
static_cast<Derived*>(this)->increment();
return *static_cast<Derived*>(this);
``Derived operator++(int);``
:Effects:
::
Derived tmp(static_cast<Derived const*>(this));
++*this;
return tmp;
``Derived& operator--();``
:Effects:
::
static_cast<Derived*>(this)->decrement();
return *static_cast<Derived*>(this);
``Derived operator--(int);``
:Effects:
::
Derived tmp(static_cast<Derived const*>(this));
--*this;
return tmp;
``Derived& operator+=(difference_type n);``
:Effects:
::
static_cast<Derived*>(this)->advance(n);
return *static_cast<Derived*>(this);
``Derived& operator-=(difference_type n);``
:Effects:
::
static_cast<Derived*>(this)->advance(-n);
return *static_cast<Derived*>(this);
``Derived operator-(difference_type n) const;``
:Effects:
::
Derived tmp(static_cast<Derived const*>(this));
return tmp -= n;
::
template <class Dr, class V, class TC, class R, class D>
Derived operator+ (iterator_facade<Dr,V,TC,R,D> const&,
typename Derived::difference_type n);
template <class Dr, class V, class TC, class R, class D>
Derived operator+ (typename Derived::difference_type n,
iterator_facade<Dr,V,TC,R,D> const&);
:Effects:
::
Derived tmp(static_cast<Derived const*>(this));
return tmp += n;
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator ==(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``((Dr1 const&)lhs).equal((Dr2 const&)rhs)``.
Otherwise,
``((Dr2 const&)rhs).equal((Dr1 const&)lhs)``.
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator !=(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``!((Dr1 const&)lhs).equal((Dr2 const&)rhs)``.
Otherwise,
``!((Dr2 const&)rhs).equal((Dr1 const&)lhs)``.
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator <(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) < 0``.
Otherwise,
``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) > 0``.
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator <=(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) <= 0``.
Otherwise,
``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) >= 0``.
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator >(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) > 0``.
Otherwise,
``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) < 0``.
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,bool>::type
operator >=(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) >= 0``.
Otherwise,
``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) <= 0``.
.. _minus:
::
template <class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
typename enable_if_interoperable<Dr1,Dr2,difference>::type
operator -(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
:Return Type:
if ``is_convertible<Dr2,Dr1>::value``
then
``difference`` shall be
``iterator_traits<Dr1>::difference_type``.
Otherwise
``difference`` shall be ``iterator_traits<Dr2>::difference_type``
:Returns:
if ``is_convertible<Dr2,Dr1>::value``
then
``-((Dr1 const&)lhs).distance_to((Dr2 const&)rhs)``.
Otherwise,
``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs)``.
|
