| Author: | David Abrahams, Jeremy Siek, Thomas Witt |
|---|---|
| Contact: | dave@boost-consulting.com, jsiek@osl.iu.edu, witt@ive.uni-hannover.de |
| Organization: | Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction |
| Date: | 2003-09-14 |
| Copyright: | Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved |
| abstract: |
|---|
The indirect iterator adapts an iterator by applying an extra dereference inside of operator*(). For example, this iterator adaptor makes it possible to view a container of pointers (e.g. list<foo*>) as if it were a container of the pointed-to type (e.g. list<foo>) .
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
);
};
The member types of indirect_iterator are defined according to the following pseudo-code. We use the abbreviation V=iterator_traits<Iterator>::value_type.:
if (Value is use_default) then
typedef iterator_traits<V>::value_type value_type;
else
typedef remove_const<Value>::type value_type;
if (Reference is use_default) then
if (Value is use_default) then
typedef iterator_traits<V>::reference reference;
else
typedef Value& reference;
else
typedef Reference reference;
if (Value is use_default) then
typedef ?? pointer;
else
typedef Value* pointer;
if (Difference is use_default)
typedef iterator_traits<Iterator>::difference_type difference_type;
else
typedef Difference difference_type;
The member indirect_iterator::iterator_category is a type that satisfies the requirements of the concepts modeled by the indirect iterator as specified in the models section.
The Iterator argument shall meet the requirements of Readable Iterator. The CategoryOrTraversal argument shall be one of the standard iterator tags or use_default. If CategoryOrTraversal is an iterator tag, the template parameter Iterator argument shall meet the traversal requirements corresponding to the iterator tag.
The expression *v, where v is an object of type iterator_traits<Iterator>::value_type, must be a valid expression and must be convertible to indirect_iterator::reference. Also indirect_iterator::reference must be convertible to indirect_iterator::value. 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.
If CategoryOrTraversal is a standard iterator tag, indirect_iterator is a model of the iterator concept corresponding to the tag, otherwise indirect_iterator satisfies the requirements of the most refined standard traversal concept that is satisfied by the Iterator argument.
indirect_iterator models Readable Iterator. If indirect_iterator::reference(*v) = t is a valid expression (where t is an object of type indirect_iterator::value_type) then indirect_iterator models Writable Iterator. If indirect_iterator::reference is a reference then indirect_iterator models Lvalue Iterator.
indirect_iterator();
| Requires: | Iterator must be Default Constructible. |
|---|---|
| Returns: | An instance of indirect_iterator with a default-constructed iterator_adaptor subobject. |
indirect_iterator(Iterator x);
| Returns: | An instance of indirect_iterator with the iterator_adaptor subobject 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. |
|---|---|
| Returns: | An instance of indirect_iterator whose iterator_adaptor subobject is constructed from y.base(). |