From Jason Turner

[range.slide.view]

C++20 → C++23 4.2 KB 133 lines
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Archived: C++20 | C++23
Markdown: C++20 | C++23
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tmp/tmpxzxjwnny/{from.md → to.md} RENAMED
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+ #### Class template `slide_view` <a id="range.slide.view">[[range.slide.view]]</a>
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+
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+ ``` cpp
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+ namespace std::ranges {
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+ template<class V>
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+ concept slide-caches-nothing = random_access_range<V> && sized_range<V>; // exposition only
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+
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+ template<class V>
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+ concept slide-caches-last = // exposition only
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+ !slide-caches-nothing<V> && bidirectional_range<V> && common_range<V>;
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+
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+ template<class V>
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+ concept slide-caches-first = // exposition only
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+ !slide-caches-nothing<V> && !slide-caches-last<V>;
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+
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+ template<forward_range V>
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+ requires view<V>
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+ class slide_view : public view_interface<slide_view<V>> {
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+ V base_; // exposition only
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+ range_difference_t<V> n_; // exposition only
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+
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+ // [range.slide.iterator], class template slide_view::iterator
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+ template<bool> class iterator; // exposition only
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+
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+ // [range.slide.sentinel], class slide_view::sentinel
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+ class sentinel; // exposition only
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+
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+ public:
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+ constexpr explicit slide_view(V base, range_difference_t<V> n);
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+
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+ constexpr V base() const & requires copy_constructible<V> { return base_; }
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+ constexpr V base() && { return std::move(base_); }
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+
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+ constexpr auto begin()
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+ requires (!(simple-view<V> && slide-caches-nothing<const V>));
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+ constexpr auto begin() const requires slide-caches-nothing<const V>;
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+
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+ constexpr auto end()
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+ requires (!(simple-view<V> && slide-caches-nothing<const V>));
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+ constexpr auto end() const requires slide-caches-nothing<const V>;
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+
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+ constexpr auto size() requires sized_range<V>;
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+ constexpr auto size() const requires sized_range<const V>;
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+ };
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+
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+ template<class R>
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+ slide_view(R&&, range_difference_t<R>) -> slide_view<views::all_t<R>>;
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+ }
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+ ```
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+
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+ ``` cpp
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+ constexpr explicit slide_view(V base, range_difference_t<V> n);
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+ ```
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+
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+ *Preconditions:* `n > 0` is `true`.
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+
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+ *Effects:* Initializes *base\_* with `std::move(base)` and *n\_* with
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+ `n`.
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+
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+ ``` cpp
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+ constexpr auto begin()
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+ requires (!(simple-view<V> && slide-caches-nothing<const V>));
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+ ```
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+
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+ *Returns:*
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+
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+ - If `V` models `slide-caches-first`,
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+ ``` cpp
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+ iterator<false>(ranges::begin(base_),
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+ ranges::next(ranges::begin(base_), n_ - 1, ranges::end(base_)), n_)
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+ ```
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+ - Otherwise,
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+ *`iterator`*`<false>(ranges::begin(`*`base_`*`), `*`n_`*`)`.
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+
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+ *Remarks:* In order to provide the amortized constant-time complexity
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+ required by the `range` concept, this function caches the result within
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+ the `slide_view` for use on subsequent calls when `V` models
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+ `slide-caches-first`.
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+
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+ ``` cpp
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+ constexpr auto begin() const requires slide-caches-nothing<const V>;
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+ ```
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+
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+ *Returns:* *`iterator`*`<true>(ranges::begin(`*`base_`*`), `*`n_`*`)`.
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+
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+ ``` cpp
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+ constexpr auto end()
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+ requires (!(simple-view<V> && slide-caches-nothing<const V>));
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+ ```
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+
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+ *Returns:*
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+
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+ - If `V` models `slide-caches-nothing`,
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+ ``` cpp
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+ iterator<false>(ranges::begin(base_) + range_difference_t<V>(size()), n_)
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+ ```
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+ - Otherwise, if `V` models `slide-caches-last`,
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+ ``` cpp
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+ iterator<false>(ranges::prev(ranges::end(base_), n_ - 1, ranges::begin(base_)), n_)
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+ ```
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+ - Otherwise, if `V` models `common_range`,
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+ ``` cpp
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+ iterator<false>(ranges::end(base_), ranges::end(base_), n_)
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+ ```
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+ - Otherwise, *`sentinel`*`(ranges::end(`*`base_`*`))`.
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+
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+ *Remarks:* In order to provide the amortized constant-time complexity
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+ required by the `range` concept, this function caches the result within
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+ the `slide_view` for use on subsequent calls when `V` models
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+ `slide-caches-last`.
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+
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+ ``` cpp
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+ constexpr auto end() const requires slide-caches-nothing<const V>;
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+ ```
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+
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+ *Returns:* `begin() + range_difference_t<const V>(size())`.
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+
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+ ``` cpp
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+ constexpr auto size() requires sized_range<V>;
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+ constexpr auto size() const requires sized_range<const V>;
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+ ```
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+
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+ *Effects:* Equivalent to:
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+
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+ ``` cpp
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+ auto sz = ranges::distance(base_) - n_ + 1;
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+ if (sz < 0) sz = 0;
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+ return to-unsigned-like(sz);
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+ ```
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+