tmp/tmpd5ay63ze/{from.md → to.md}
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| 1 |
+
#### General <a id="view.interface.general">[[view.interface.general]]</a>
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The class template `view_interface` is a helper for defining view-like
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types that offer a container-like interface. It is parameterized with
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| 5 |
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the type that is derived from it.
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``` cpp
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+
namespace std::ranges {
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template<class D>
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requires is_class_v<D> && same_as<D, remove_cv_t<D>>
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class view_interface {
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private:
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constexpr D& derived() noexcept { // exposition only
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return static_cast<D&>(*this);
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}
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constexpr const D& derived() const noexcept { // exposition only
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return static_cast<const D&>(*this);
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}
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public:
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constexpr bool empty() requires sized_range<D> || forward_range<D> {
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if constexpr (sized_range<D>)
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return ranges::size(derived()) == 0;
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else
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return ranges::begin(derived()) == ranges::end(derived());
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}
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constexpr bool empty() const requires sized_range<const D> || forward_range<const D> {
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if constexpr (sized_range<const D>)
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return ranges::size(derived()) == 0;
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else
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return ranges::begin(derived()) == ranges::end(derived());
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}
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constexpr auto cbegin() requires input_range<D> {
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return ranges::cbegin(derived());
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}
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constexpr auto cbegin() const requires input_range<const D> {
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return ranges::cbegin(derived());
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}
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constexpr auto cend() requires input_range<D> {
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return ranges::cend(derived());
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}
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constexpr auto cend() const requires input_range<const D> {
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return ranges::cend(derived());
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}
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constexpr explicit operator bool()
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requires requires { ranges::empty(derived()); } {
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return !ranges::empty(derived());
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}
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constexpr explicit operator bool() const
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requires requires { ranges::empty(derived()); } {
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return !ranges::empty(derived());
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}
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constexpr auto data() requires contiguous_iterator<iterator_t<D>> {
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return to_address(ranges::begin(derived()));
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}
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constexpr auto data() const
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requires range<const D> && contiguous_iterator<iterator_t<const D>> {
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return to_address(ranges::begin(derived()));
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}
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constexpr auto size() requires forward_range<D> &&
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sized_sentinel_for<sentinel_t<D>, iterator_t<D>> {
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| 66 |
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return to-unsigned-like(ranges::end(derived()) - ranges::begin(derived()));
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}
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constexpr auto size() const requires forward_range<const D> &&
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sized_sentinel_for<sentinel_t<const D>, iterator_t<const D>> {
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return to-unsigned-like(ranges::end(derived()) - ranges::begin(derived()));
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}
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constexpr decltype(auto) front() requires forward_range<D>;
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constexpr decltype(auto) front() const requires forward_range<const D>;
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constexpr decltype(auto) back() requires bidirectional_range<D> && common_range<D>;
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constexpr decltype(auto) back() const
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requires bidirectional_range<const D> && common_range<const D>;
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+
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template<random_access_range R = D>
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constexpr decltype(auto) operator[](range_difference_t<R> n) {
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return ranges::begin(derived())[n];
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}
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template<random_access_range R = const D>
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constexpr decltype(auto) operator[](range_difference_t<R> n) const {
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return ranges::begin(derived())[n];
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}
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};
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}
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```
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The template parameter `D` for `view_interface` may be an incomplete
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type. Before any member of the resulting specialization of
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`view_interface` other than special member functions is referenced, `D`
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shall be complete, and model both `derived_from<view_interface<D>>` and
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`view`.
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