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25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

25.7.10 Take view [range.take]

25.7.10.2 Class template take_view [range.take.view]

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namespace std::ranges { template<view V> class take_view : public view_interface<take_view<V>> { private: V base_ = V(); // exposition only range_difference_t<V> count_ = 0; // exposition only // [range.take.sentinel], class template take_view​::​sentinel template<bool> class sentinel; // exposition only public: take_view() requires default_initializable<V> = default; constexpr explicit take_view(V base, range_difference_t<V> count); constexpr V base() const & requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr auto begin() requires (!simple-view<V>) { if constexpr (sized_range<V>) { if constexpr (random_access_range<V>) { return ranges::begin(base_); } else { auto sz = range_difference_t<V>(size()); return counted_iterator(ranges::begin(base_), sz); } } else if constexpr (sized_sentinel_for<sentinel_t<V>, iterator_t<V>>) { auto it = ranges::begin(base_); auto sz = std::min(count_, ranges::end(base_) - it); return counted_iterator(std::move(it), sz); } else { return counted_iterator(ranges::begin(base_), count_); } } constexpr auto begin() const requires range<const V> { if constexpr (sized_range<const V>) { if constexpr (random_access_range<const V>) { return ranges::begin(base_); } else { auto sz = range_difference_t<const V>(size()); return counted_iterator(ranges::begin(base_), sz); } } else if constexpr (sized_sentinel_for<sentinel_t<const V>, iterator_t<const V>>) { auto it = ranges::begin(base_); auto sz = std::min(count_, ranges::end(base_) - it); return counted_iterator(std::move(it), sz); } else { return counted_iterator(ranges::begin(base_), count_); } } constexpr auto end() requires (!simple-view<V>) { if constexpr (sized_range<V>) { if constexpr (random_access_range<V>) return ranges::begin(base_) + range_difference_t<V>(size()); else return default_sentinel; } else if constexpr (sized_sentinel_for<sentinel_t<V>, iterator_t<V>>) { return default_sentinel; } else { return sentinel<false>{ranges::end(base_)}; } } constexpr auto end() const requires range<const V> { if constexpr (sized_range<const V>) { if constexpr (random_access_range<const V>) return ranges::begin(base_) + range_difference_t<const V>(size()); else return default_sentinel; } else if constexpr (sized_sentinel_for<sentinel_t<const V>, iterator_t<const V>>) { return default_sentinel; } else { return sentinel<true>{ranges::end(base_)}; } } constexpr auto size() requires sized_range<V> { auto n = ranges::size(base_); return ranges::min(n, static_cast<decltype(n)>(count_)); } constexpr auto size() const requires sized_range<const V> { auto n = ranges::size(base_); return ranges::min(n, static_cast<decltype(n)>(count_)); } constexpr auto reserve_hint() { if constexpr (approximately_sized_range<V>) { auto n = static_cast<range_difference_t<V>>(ranges::reserve_hint(base_)); return to-unsigned-like(ranges::min(n, count_)); } return to-unsigned-like(count_); } constexpr auto reserve_hint() const { if constexpr (approximately_sized_range<const V>) { auto n = static_cast<range_difference_t<const V>>(ranges::reserve_hint(base_)); return to-unsigned-like(ranges::min(n, count_)); } return to-unsigned-like(count_); } }; template<class R> take_view(R&&, range_difference_t<R>) -> take_view<views::all_t<R>>; }
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constexpr explicit take_view(V base, range_difference_t<V> count);
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Preconditions: count >= 0 is true.
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Effects: Initializes base_ with std​::​move(base) and count_ with count.