From Jason Turner

[view.interface]

C++17 → C++20 3.8 KB 102 lines
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Archived: C++17 | C++20
Markdown: C++17 | C++20
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  1. tmp/tmpr_gherq_/{from.md → to.md} +99 -0
tmp/tmpr_gherq_/{from.md → to.md} RENAMED
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+ ### View interface <a id="view.interface">[[view.interface]]</a>
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+
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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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+ the type that is derived from it.
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+
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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 : public view_base {
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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 forward_range<D> {
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+ return ranges::begin(derived()) == ranges::end(derived());
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+ }
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+ constexpr bool empty() const requires forward_range<const D> {
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+ return ranges::begin(derived()) == ranges::end(derived());
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+ }
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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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+
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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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+
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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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+ return 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 ranges::end(derived()) - ranges::begin(derived());
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+ }
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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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+
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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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+
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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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+
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+ #### Members <a id="view.interface.members">[[view.interface.members]]</a>
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+
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+ ``` cpp
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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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+ ```
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+
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+ *Preconditions:* `!empty()`.
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+
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+ *Effects:* Equivalent to: `return *ranges::begin(`*`derived`*`());`
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+
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+ ``` cpp
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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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+
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+ *Preconditions:* `!empty()`.
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+
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+ *Effects:* Equivalent to:
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+ `return *ranges::prev(ranges::end(`*`derived`*`()));`
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+