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[SVN r1187]
This commit is contained in:
Jeremy Siek
2003-04-25 17:10:22 +00:00
parent 46daf8053b
commit 20eeff2372
2 changed files with 119 additions and 125 deletions
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130
doc/facade-and-adaptor.rst
View File

@@ -361,6 +361,16 @@ Standard compliant iterators).
Proposed Text
===============
Two forward traversal iterator types ``X`` and ``Y`` are
*interoperable* if one and only one is convertible to the other and
for any object ``x`` of type ``X`` and ``y`` of type ``Y``, if ``x ==
y``, ``y == x``, ``x != y``, ``y != x`` are well-defined. Two random
access traversal iterators are *interoperable* if, in addition,
``<``,``<=``,``>=``,``>``, and - are well-defined.
Header ``<iterator_helper>`` synopsis [lib.iterator.helper.synopsis]
=======================================================================
@@ -430,39 +440,9 @@ Header ``<iterator_helper>`` synopsis [lib.iterator.helper.synopsis]
Iterator facade [lib.iterator.facade]
=====================================
The iterator requirements define a rich interface, containing many
redundant operators, so that using iterators is convenient. The
``iterator_facade`` class template makes it easier to create iterators
by implementing the rich interface of standard iterators in terms of a
few core functions. The user of ``iterator_facade`` derives his
iterator class from an instantiation of ``iterator_facade`` and
defines member functions implementing the core behaviors.
.. Jeremy, I think this text is rather inappropriate for the
standard. This is not the place to discuss motivation, for
example. Compare with the standard text for vector:
1 A vector is a kind of sequence that supports random access
iterators. In addition, it supports (amortized) constant time
insert and erase operations at the end; insert and erase in the
middle take linear time. Storage management is handled
automatically, though hints can be given to improve efficiency.
2 A vector satisfies all of the requirements of a container and
of a reversible container (given in two tables in 23.1) and of a
sequence, including most of the optional sequence requirements
(23.1.1). The exceptions are the push_front and pop_front member
functions, which are not provided. Descriptions are pro- vided
here only for operations on vector that are not described in one
of these tables or for operations where there is additional
semantic information.
I suggest, instead:
``iterator_facade`` is a base class template which implements the
interface of standard iterators in terms of a few core functions
and associated types, to be supplied by a derived iterator class.
``iterator_facade`` is a base class template which implements the
interface of standard iterators in terms of a few core functions
and associated types, to be supplied by a derived iterator class.
Template class ``iterator_facade``
----------------------------------
@@ -579,7 +559,7 @@ object of type ``X``, ``b`` and ``c`` are objects of type ``const X``,
``n`` is an object of ``X::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.
interoperable with ``X``.
+----------------------------------------+----------------------------------------+-------------------------------------------------+-------------------------------------------+
| Expression | Return Type | Assertion/Note/Precondition/Postcondition | Required to implement Iterator Concept(s) |
@@ -706,33 +686,15 @@ interoperable with X.
Iterator adaptor [lib.iterator.adaptor]
=======================================
.. Jeremy, the same argument about appropriateness applies here as well.
The ``iterator_adaptor`` is a base class template which is a derived
class of ``iterator_facade``. The core interface functions expected by
``iterator_facade`` are implemented in terms of the ``Base`` template
parameter. A class derived from ``iterator_adaptor`` typically
overrides some of the (non-vertual) core interface functions to adapt
the behaviour of the iterator. The ``Base`` type need not meet the
full requirements for an iterator. It need only support the operations
that are not overriden by the users derived class.
A common pattern of iterator construction is the adaptation of one
iterator to form a new one. The functionality of an iterator is
composed of four orthogonal aspects: traversal, indirection, equality
comparison, and distance measurement. Adapting an old iterator to
create a new one often saves work because one can change a few aspects
of the functionality while retaining the rest. For example, the
Standard provides ``reverse_iterator``, which adapts any Bidirectional
Iterator by inverting its direction of traversal.
The ``iterator_adaptor`` class template fulfills the need for
constructing adaptors. Instantiations of ``iterator_adaptor`` serve
as a base classes for new iterators, providing the default behaviour
of forwarding all operations to the underlying iterator. The user can
selectively replace these features in the derived iterator class.
The ``iterator_adaptor`` class template adapts a ``Base`` type to
create a new iterator ("base" here means the type being adapted).
The ``iterator_adaptor`` forwards all operations to an instance of the
``Base`` type, which it stores as a member. The user of
``iterator_adaptor`` creates a class derived from an instantiation of
``iterator_adaptor`` and then selectively overrides some of the core
operations by implementing the (non-virtual) member functions
described in [lib.iterator.facade]. The ``Base`` type need not meet
the full requirements for an iterator. It need only support the
operations that are not overriden by the users derived class.
Template class ``iterator_adaptor``
-----------------------------------
@@ -756,21 +718,61 @@ Template class ``iterator_adaptor``
iterator_adaptor() {}
explicit iterator_adaptor(Base iter);
Base base() const;
protected:
// Default implementation of core interface for iterator_facade
typename super_t::reference dereference() const
{ return *m_iterator; }
template <
class OtherDerived, class OtherIterator, class V, class C, class R, class P, class D
>
bool equal(iterator_adaptor<OtherDerived, OtherIterator, V, C, R, P, D> const& x) const
{
BOOST_STATIC_ASSERT(
(detail::same_category_and_difference<Derived,OtherDerived>::value)
);
return m_iterator == x.base();
}
void advance(typename super_t::difference_type n)
{
m_iterator += n;
}
void increment() { ++m_iterator; }
void decrement() { --m_iterator; }
template <
class OtherDerived, class OtherIterator, class V, class C, class R, class P, class D
>
typename super_t::difference_type distance_to(
iterator_adaptor<OtherDerived, OtherIterator, V, C, R, P, D> const& y) const
{
BOOST_STATIC_ASSERT(
(detail::same_category_and_difference<Derived,OtherDerived>::value)
);
return y.base() - m_iterator;
}
Base const& base_reference() const
{ return m_iterator; }
private: // exposition
Base m_iterator;
};
``iterator_adaptor`` requirements
---------------------------------
Write me.
.. Make sure to mention that this words for both old and new
.. Make sure to mention that this works for both old and new
style iterators. -JGS
.. I'm not sure we should say that in the standard text; let other
people add non-normative in editing if they feel the need
;-) -DWA
.. Well, we have to specify the requirements for the template
parameters such as ``Category``, so this will come up. -JGS
Specialized adaptors [lib.iterator.special.adaptors]
====================================================
@@ -871,6 +873,8 @@ indirect iterator.
new categories. I think it only applies to the traversal part of
the concept.
.. Address the above. -JGS
Reverse iterator
----------------

114
doc/new-iter-concepts.rst
View File

@@ -579,39 +579,29 @@ pseudo-code.
::
inherit-category(access-tag, traversal-tag) =
(access-tag is convertible to readable_lvalue_iterator_tag
or access-tag is convertible to writable_lvalue_iterator_tag
)
? (
(traversal-tag is convertible to random_access_traversal_tag)
? random_access_iterator_tag
: (traversal-tag is convertible to bidirectional_traversal_tag)
? bidirectional_iterator_tag
: (traversal-tag is convertible to forward_traversal_tag)
? forward_iterator_tag
: null_category_tag
)
: (access-tag is convertible to readable_writable_iterator_tag
and traversal-tag is convertible to single_pass_iterator_tag)
? input_output_iterator_tag
: (access-tag is convertible to readable_iterator_tag
and traversal-tag is convertible to single_pass_iterator_tag)
? input_iterator_tag
: (access-tag is convertible to writable_iterator_tag
and traversal-tag is convertible to incrementable_iterator_tag)
? output_iterator_tag
: null_category_tag;
.. Jeremy, I'm not attached to the rewrite above; I just did it to see
if I could make it clearer please feel free to rewrite if you don't
like it.
inherit-category(access-tag, traversal-tag) =
if (access-tag is convertible to readable_lvalue_iterator_tag
or access-tag is convertible to writable_lvalue_iterator_tag) {
if (traversal-tag is convertible to random_access_traversal_tag)
return random_access_iterator_tag;
else if (traversal-tag is convertible to bidirectional_traversal_tag)
return bidirectional_iterator_tag;
else if (traversal-tag is convertible to forward_traversal_tag)
return forward_iterator_tag;
else
return null_category_tag;
} else if (access-tag is convertible to readable_writable_iterator_tag
and traversal-tag is convertible to single_pass_iterator_tag)
return input_output_iterator_tag;
else if (access-tag is convertible to readable_iterator_tag
and traversal-tag is convertible to single_pass_iterator_tag)
return input_iterator_tag;
else if (access-tag is convertible to writable_iterator_tag
and traversal-tag is convertible to incrementable_iterator_tag)
return output_iterator_tag;
else
return null_category_tag;
The ``access_category`` and ``traversal_category`` class templates are
traits classes. For iterators whose
@@ -626,38 +616,38 @@ The following pseudo-code describes the algorithm.
::
access-category(Iterator) =
cat = iterator_traits<Iterator>::iterator_category;
if (cat == iterator_tag<Access,Traversal>)
return Access;
else if (cat is convertible to forward_iterator_tag) {
if (iterator_traits<Iterator>::reference is a const reference)
return readable_lvalue_iterator_tag;
cat = iterator_traits<Iterator>::iterator_category;
if (cat == iterator_tag<Access,Traversal>)
return Access;
else if (cat is convertible to forward_iterator_tag) {
if (iterator_traits<Iterator>::reference is a const reference)
return readable_lvalue_iterator_tag;
else
return writable_lvalue_iterator_tag;
} else if (cat is convertible to input_iterator_tag)
return readable_iterator_tag;
else if (cat is convertible to output_iterator_tag)
return writable_iterator_tag;
else
return writable_lvalue_iterator_tag;
} else if (cat is convertible to input_iterator_tag)
return readable_iterator_tag;
else if (cat is convertible to output_iterator_tag)
return writable_iterator_tag;
else
return null_category_tag;
return null_category_tag;
traversal-category(Iterator) =
cat = iterator_traits<Iterator>::iterator_category;
if (cat == iterator_tag<Access,Traversal>)
return Traversal;
else if (cat is convertible to random_access_iterator_tag)
return random_access_traversal_tag;
else if (cat is convertible to bidirectional_iterator_tag)
return bidirectional_traversal_tag;
else if (cat is convertible to forward_iterator_tag)
return forward_traversal_tag;
else if (cat is convertible to input_iterator_tag)
return single_pass_iterator_tag;
else if (cat is convertible to output_iterator_tag)
return incrementable_iterator_tag;
else
return null_category_tag;
};
cat = iterator_traits<Iterator>::iterator_category;
if (cat == iterator_tag<Access,Traversal>)
return Traversal;
else if (cat is convertible to random_access_iterator_tag)
return random_access_traversal_tag;
else if (cat is convertible to bidirectional_iterator_tag)
return bidirectional_traversal_tag;
else if (cat is convertible to forward_iterator_tag)
return forward_traversal_tag;
else if (cat is convertible to input_iterator_tag)
return single_pass_iterator_tag;
else if (cat is convertible to output_iterator_tag)
return incrementable_iterator_tag;
else
return null_category_tag;
The following specializations provide the access and traversal
category tags for pointer types.