-
+
In the tables below, X is an iterator type, a and b are
constant objects of type X, r and s are mutable objects of
type X, T is std::iterator_traits<X>::value_type, and
v is a constant object of type T.
-
+
A class or built-in type X models the Incrementable Iterator
concept if the following expressions are valid and respect the stated
semantics.
@@ -557,7 +520,7 @@ semantics.
-
+
A class or built-in type X models the Single Pass Iterator
concept if the following expressions are valid and respect the stated
semantics.
@@ -602,7 +565,7 @@ its domain
-
+
A class or built-in type X models the Forward Traversal Iterator
concept if the following expressions are valid and respect the stated
semantics.
@@ -648,7 +611,7 @@ the distance between iterators
-
+
A class or built-in type X models the Bidirectional Traversal
Iterator concept if the following expressions are valid and respect
the stated semantics.
@@ -690,7 +653,7 @@ dereferenceable.
--(++r)
-
+
A class or built-in type X models the Random Access Traversal
Iterator concept if the following expressions are valid and respect
the stated semantics. In the table below, Distance is
@@ -805,31 +768,23 @@ relation
-
+
// lib.iterator.traits, traits and tags
-template <class Iterator> struct access_category;
+template <class Iterator> struct is_readable;
+template <class Iterator> struct is_writable;
+template <class Iterator> struct is_swappable;
template <class Iterator> struct traversal_category;
-template <class AccessTag, class TraversalTag>
+enum iterator_access { readable_iterator = 1, writable_iterator = 2,
+ swappable_iterator = 4, lvalue_iterator = 8 };
+
+template <iterator_access x, class TraversalTag>
struct iterator_tag : /* appropriate old category or categories */ {
- typedef AccessTag access;
+ static const iterator_access access = x;
typedef TraversalTag traversal;
};
-struct readable_iterator_tag { };
-struct writable_iterator_tag { };
-struct swappable_iterator_tag { };
-struct readable_writable_iterator_tag
- : virtual readable_iterator_tag
- , virtual writable_iterator_tag
- , virtual swappable_iterator_tag { };
-struct readable_lvalue_iterator_tag
- : virtual readable_iterator_tag { };
-struct writable_lvalue_iterator_tag
- : virtual public readable_writable_iterator_tag
- , virtual public readable_lvalue_iterator_tag { };
-
struct incrementable_iterator_tag { };
struct single_pass_iterator_tag : incrementable_iterator_tag { };
struct forward_traversal_tag : single_pass_iterator_tag { };
@@ -841,15 +796,15 @@ struct input_output_iterator_tag : input_iterator_tag, output_iterator_tag {};
-
+
The iterator_tag class template is an iterator category tag that
-encodes the access and traversal tags in addition to being compatible
+encodes the access enum and traversal tag in addition to being compatible
with the original iterator tags. The iterator_tag class inherits
from one of the original iterator tags according to the following
pseudo-code.
-inherit-category(access-tag, traversal-tag) =
- if (access-tag is convertible to readable_lvalue_iterator_tag) {
+inherit-category(access, traversal-tag) =
+ if (access & lvalue_iterator) {
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)
@@ -861,52 +816,64 @@ inherit-category(access-tag, traversal-tag) =
return input_output_iterator_tag;
else
return input_iterator_tag;
- else if (access-tag is convertible to writable_iterator_tag)
+ else if (access & writable_iterator)
return output_iterator_tag;
else
return null_category_tag;
- } else if (access-tag is convertible to readable_writable_iterator_tag
+ } else if ((access & readable_iterator) and (access & writable_iterator)
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
+ else if (access & readable_iterator
and traversal-tag is convertible to single_pass_iterator_tag)
return input_iterator_tag;
- else if (access-tag is convertible to writable_iterator_tag
+ else if (access & writable_iterator
and traversal-tag is convertible to incrementable_iterator_tag)
return output_iterator_tag;
else
return null_category_tag;
-
If the argument for the template parameter AccessTag is not
-convertible to one or more of: readable_iterator_tag,
-writable_iterator_tag, swappable_iterator_tag, or if the
-argument for TraversalTag is not convertible to
+
If the argument for TraversalTag is not convertible to
incrementable_iterator_tag then the programm is ill-formed.
-
The access_category and traversal_category class templates are
-traits classes. For iterators whose
-iterator_traits<Iter>::iterator_category type is iterator_tag,
-the access_category and traversal_category traits access the
-access and traversal member types within iterator_tag.
-For iterators whose iterator_traits<Iter>::iterator_category type
-is not iterator_tag and instead is a tag convertible to one of the
-original tags, the appropriate traversal and access tags is deduced.
-The following pseudo-code describes the algorithm.
+
The is_readable, is_writable, is_swappable, and
+traversal_category class templates are traits classes. For
+iterators whose iterator_traits<Iter>::iterator_category type is
+iterator_tag, these traits obtain the access enum and
+traversal member type from within iterator_tag. For iterators
+whose iterator_traits<Iter>::iterator_category type is not
+iterator_tag and instead is a tag convertible to one of the
+original tags, the appropriate traversal tag and access bits are
+deduced. The following pseudo-code describes the algorithm.
-access-category(Iterator) =
+is-readable(Iterator) =
cat = iterator_traits<Iterator>::iterator_category;
if (cat == iterator_tag<Access,Traversal>)
- return Access;
+ return Access % readable_iterator;
+ else if (cat is convertible to input_iterator_tag)
+ return true;
+ else
+ return false;
+
+is-writable(Iterator) =
+ cat = iterator_traits<Iterator>::iterator_category;
+ if (cat == iterator_tag<Access,Traversal>)
+ return Access % writable_iterator;
+ else if (cat is convertible to forward_iterator_tag
+ or output_iterator_tag)
+ return true;
+ else
+ return false;
+
+is-swappable(Iterator) =
+ cat = iterator_traits<Iterator>::iterator_category;
+ if (cat == iterator_tag<Access,Traversal>)
+ return Access % swappable_iterator;
else if (cat is convertible to forward_iterator_tag) {
if (iterator_traits<Iterator>::reference is a const reference)
- return readable_lvalue_iterator_tag;
+ return false;
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 true;
+ } else
+ return false;
traversal-category(Iterator) =
cat = iterator_traits<Iterator>::iterator_category;
@@ -929,15 +896,18 @@ traversal-category(Iterator) =
category tags for pointer types.
template <typename T>
-struct access_category<const T*>
-{
- typedef readable_lvalue_iterator_tag type;
-};
+struct is_readable<const T*> { typedef true_type type; };
template <typename T>
-struct access_category<T*>
-{
- typedef writable_lvalue_iterator_tag type;
-};
+struct is_writable<const T*> { typedef false_type type; };
+template <typename T>
+struct is_swappable<const T*> { typedef false_type type; };
+
+template <typename T>
+struct is_readable<T*> { typedef true_type type; };
+template <typename T>
+struct is_writable<T*> { typedef true_type type; };
+template <typename T>
+struct is_swappable<T*> { typedef true_type type; };
template <typename T>
struct traversal_category<T*>
