We provide an access mechanism for mapping iterator types to the new -traversal tags and access bitfield. Our design reuses +traversal tags and access bit field. Our design reuses iterator_traits<Iter>::iterator_category as the access mechanism. To that end, the access and traversal information is bundled into a single type using the following iterator_tag class.
@@ -284,17 +284,28 @@ enum iterator_access { readable_iterator = 1, writable_iterator = 2, template <unsigned int access_bits, class TraversalTag> struct iterator_tag : /* appropriate old category or categories */ { - static const iterator_access access = (iterator_access)access_bits; + static const iterator_access access = + (iterator_access)access_bits & + (readable_iterator | writable_iterator | swappable_iterator); typedef TraversalTag traversal; }; +The access_bits argument is declared to be unsigned int +instead of the enum iterator_access for convenience of use. For +example, the expression (readable_iterator | writable_iterator) +produces an unsigned int, not an iterator_access. The purpose of +the lvalue_iterator part of the iterator_access enum is to +communicate to iterator_tag whether the reference type is an +lvalue so that the appropriate old category can be chosen for the base +class. The lvalue_iterator bit is not recorded in the +iterator_tag::access data member.
The iterator_tag class template is derived from the appropriate iterator tag or tags from the old requirements based on the new-style tags passed as template parameters. The algorithm for determining the old tag or tags from the new tags picks the least-refined old concepts that include all of the requirements of the access and traversal concepts (that is, the closest fit), if any such category exists. For -example, a the category tag for a Readable Single Pass Iterator will +example, the category tag for a Readable Single Pass Iterator will always be derived from input_iterator_tag, while the category tag for a Single Pass Iterator that is both Readable and Writable will be derived from both input_iterator_tag and output_iterator_tag.
@@ -303,14 +314,12 @@ obtain the access and traversal characteristics of an iterator. These helper classes work both for iterators whose iterator_category is iterator_tag and also for iterators using the original iterator categories. -template <class Iterator> struct is_readable { typedef ... type; }; +
+template <class Iterator> struct is_readable { typedef ... type; };
template <class Iterator> struct is_writable { typedef ... type; };
template <class Iterator> struct is_swappable { typedef ... type; };
-template <class Iterator> struct traversal_category { typedef ... type; };
-We do not include a helper class is_lvalue_iterator because that can easily be deduced by checking whether iterator_traits<Iterator>::reference is a real reference.
@@ -860,12 +869,8 @@ inherit-category(access, traversal-tag) = else return null_category_tag; -The access argument is declared to be unsigned int instead of the -enum iterator_access for convenience of use. For example, the -expression (readable_iterator | writable_iterator) produces an -unsigned int, not iterator_access. If the argument for -TraversalTag is not convertible to incrementable_iterator_tag -then the programm is ill-formed.
+If the argument for TraversalTag is not convertible to +incrementable_iterator_tag then the program is ill-formed.
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
@@ -953,7 +958,7 @@ LocalWords: ConstantLvalueIterator MutableLvalueIterator CopyConstructible TR
LocalWords: ForwardTraversalIterator BidirectionalTraversalIterator lvalue
LocalWords: RandomAccessTraversalIterator dereferenceable Incrementable tmp
LocalWords: incrementable xxx min prev inplace png oldeqnew AccessTag struct
-LocalWords: TraversalTag typename lvalues DWA Hmm JGS -->
+LocalWords: TraversalTag typename lvalues DWA Hmm JGS mis enum -->
diff --git a/doc/new-iter-concepts.rst b/doc/new-iter-concepts.rst
index 7d77512..44642f7 100644
--- a/doc/new-iter-concepts.rst
+++ b/doc/new-iter-concepts.rst
@@ -251,10 +251,10 @@ inheritance so that a tag is convertible to another tag if the concept
associated with the first tag is a refinement of the second tag.
Since the access concepts are not related via refinement, but instead
cover orthogonal issues, we do not use tags for the access concepts,
-but instead use the equivalent of a bitfield.
+but instead use the equivalent of a bit field.
We provide an access mechanism for mapping iterator types to the new
-traversal tags and access bitfield. Our design reuses
+traversal tags and access bit field. Our design reuses
``iterator_traits