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common_iterator: expose iterator_traits aliases #1660

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common_iterator: expose iterator_traits aliases #1660

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75 changes: 40 additions & 35 deletions include/range/v3/iterator/common_iterator.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,40 @@ namespace ranges
{
return that.data_;
}

template<typename I>
auto demote_common_iter_cat(...) -> nil_;
template<typename I>
auto demote_common_iter_cat(long)
-> with_iterator_category<std::input_iterator_tag>;
template(typename I)(
/// \pre
requires derived_from<typename std::iterator_traits<I>::iterator_category,
std::forward_iterator_tag>)
auto demote_common_iter_cat(int)
-> with_iterator_category<std::forward_iterator_tag>;

template<typename I, bool = (bool)input_iterator<I>>
struct common_iterator_std_traits : decltype(detail::demote_common_iter_cat<I>(0))
{
using difference_type = iter_difference_t<I>;
using value_type = iter_value_t<I>;
using reference = iter_reference_t<I>;
using pointer = detail::iter_pointer_t<I>;
using iterator_concept =
meta::conditional_t<(bool)forward_iterator<I>, std::forward_iterator_tag,
std::input_iterator_tag>;
};

template<typename I>
struct common_iterator_std_traits<I, false>
{
using difference_type = iter_difference_t<I>;
using value_type = void;
using reference = void;
using pointer = void;
using iterator_category = std::output_iterator_tag;
};
} // namespace detail

#if RANGES_BROKEN_CPO_LOOKUP
Expand Down Expand Up @@ -125,8 +159,13 @@ namespace ranges
return arrow_proxy_(*j);
}

using traits = detail::common_iterator_std_traits<I>;
public:
using difference_type = iter_difference_t<I>;
using difference_type = typename traits::difference_type;
using value_type = typename traits::value_type;
using pointer = typename traits::pointer;
using reference = typename traits::reference;
using iterator_category = typename traits::iterator_category;

common_iterator() = default;
common_iterator(I i)
Expand Down Expand Up @@ -330,40 +369,6 @@ namespace ranges
/// \cond
namespace detail
{
template<typename I>
auto demote_common_iter_cat(...) -> nil_;
template<typename I>
auto demote_common_iter_cat(long)
-> with_iterator_category<std::input_iterator_tag>;
template(typename I)(
/// \pre
requires derived_from<typename std::iterator_traits<I>::iterator_category,
std::forward_iterator_tag>)
auto demote_common_iter_cat(int)
-> with_iterator_category<std::forward_iterator_tag>;

template<typename I, bool = (bool)input_iterator<I>>
struct common_iterator_std_traits : decltype(detail::demote_common_iter_cat<I>(0))
{
using difference_type = iter_difference_t<I>;
using value_type = iter_value_t<I>;
using reference = iter_reference_t<I>;
using pointer = detail::iter_pointer_t<I>;
using iterator_concept =
meta::conditional_t<(bool)forward_iterator<I>, std::forward_iterator_tag,
std::input_iterator_tag>;
};

template<typename I>
struct common_iterator_std_traits<I, false>
{
using difference_type = iter_difference_t<I>;
using value_type = void;
using reference = void;
using pointer = void;
using iterator_category = std::output_iterator_tag;
};

// An iterator adaptor that demotes a user-defined difference_type to
// std::intmax_t, for use when constructing containers from such
// iterators.
Expand Down