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Fixed a bug in reference type and category computation.

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Improved comments.


[SVN r1291]
This commit is contained in:
Dave Abrahams
2003-05-29 22:33:10 +00:00
parent 5076d782af
commit 1236797033
1 changed files with 42 additions and 48 deletions
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90
include/boost/iterator/iterator_adaptor.hpp
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@@ -120,54 +120,24 @@ namespace boost
# endif
//
// iterator_traits_adaptor can be used to create new iterator traits by adapting
// the traits of a given iterator type. Together with iterator_adaptor it simplifies
// the creation of adapted iterator types. Therefore the ordering the template
// argument ordering is different from the std::iterator template, so that default
// arguments can be used effectivly.
//
// The ordering changed slightly with respect to former versions of iterator_adaptor
// The idea is that when the user needs to fiddle with the reference type
// it is highly likely that the iterator category has to be adjusted as well
//
// Value - if supplied, the value_type of the resulting iterator, unless
// const. If const, a conforming compiler strips constness for the
// value_type. If not supplied, iterator_traits<Base>::value_type is used
//
// Reference - the reference type of the resulting iterator, and in
// particular, the result type of operator*(). If not supplied but
// Value is supplied, Value& is used. Otherwise
// iterator_traits<Base>::reference is used.
//
// Pointer - the pointer type of the resulting iterator, and in
// particular, the result type of operator->(). If not
// supplied but Value is supplied, Value* is used. Otherwise
// iterator_traits<Base>::pointer is used.
//
// Category - the iterator_category of the resulting iterator. If not
// supplied, iterator_traits<Base>::iterator_category is used.
//
// Distance - the difference_type of the resulting iterator. If not
// supplied, iterator_traits<Base>::difference_type is used.
//
// TODO
// ? Automatic adjustment of category ?
// Default template argument handling for iterator_adaptor
//
namespace detail
{
template <class T, class Condition, class DefaultNullaryFn>
// If T is use_default, return the result of invoking
// DefaultNullaryFn, otherwise return T.
template <class T, class DefaultNullaryFn>
struct ia_dflt_help
: mpl::apply_if<
mpl::and_<
is_same<T, use_default>
, Condition
>
is_same<T, use_default>
, DefaultNullaryFn
, mpl::identity<T>
>
{
};
// A metafunction which computes an iterator_adaptor's base class,
// a specialization of iterator_facade.
template <
class Derived
, class Base
@@ -178,42 +148,66 @@ namespace boost
>
struct iterator_adaptor_base
{
private:
private: // intermediate results
typedef typename detail::ia_dflt_help<
Category, mpl::true_, BOOST_ITERATOR_CATEGORY<Base>
Category, BOOST_ITERATOR_CATEGORY<Base>
>::type category;
typedef typename detail::ia_dflt_help<
Reference, is_same<Value, use_default>, iterator_reference<Base>
Reference
, mpl::apply_if<
is_same<Value, use_default>
, iterator_reference<Base>
, mpl::identity<Value&>
>
>::type reference;
public:
public: // return type
typedef iterator_facade<
Derived
, typename detail::ia_dflt_help<
Value, mpl::true_, iterator_value<Base>
Value, iterator_value<Base>
>::type
, typename access_category_tag<category, reference>::type
, typename traversal_category_tag<category>::type
, typename detail::ia_dflt_help<
Reference, is_same<Value, use_default>, iterator_reference<Base>
>::type
, reference
, typename detail::ia_dflt_help<
Difference, mpl::true_, iterator_difference<Base>
Difference, iterator_difference<Base>
>::type
>
type;
};
}
//
// Iterator Adaptor
//
// The parameter ordering changed slightly with respect to former
// versions of iterator_adaptor The idea is that when the user needs
// to fiddle with the reference type it is highly likely that the
// iterator category has to be adjusted as well. Any of the
// following four template arguments may be ommitted or explicitly
// replaced by use_default.
//
// Value - if supplied, the value_type of the resulting iterator, unless
// const. If const, a conforming compiler strips constness for the
// value_type. If not supplied, iterator_traits<Base>::value_type is used
//
// Category - the iterator_category of the resulting iterator. If not
// supplied, iterator_traits<Base>::iterator_category is used.
//
// Reference - the reference type of the resulting iterator, and in
// particular, the result type of operator*(). If not supplied but
// Value is supplied, Value& is used. Otherwise
// iterator_traits<Base>::reference is used.
//
// Difference - the difference_type of the resulting iterator. If not
// supplied, iterator_traits<Base>::difference_type is used.
//
template <
class Derived