24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.8 Take while view [range.take.while]

24.7.8.1 Overview [range.take.while.overview]

Given a unary predicate pred and a view r, take_while_view produces a view of the range [begin(r), ranges::find_if_not(r, pred)).

The name views::take_while denotes a range adaptor object ([range.adaptor.object]).

Given subexpressions E and F, the expression views::take_while(E, F) is expression-equivalent to take_while_view{E, F}.

[Example 1: auto input = istringstream{"0 1 2 3 4 5 6 7 8 9"}; auto small = [](const auto x) noexcept { return x < 5; }; auto small_ints = istream_view<int>(input) | views::take_while(small); for (const auto i : small_ints) { cout << i << ' '; // prints 0 1 2 3 4 } auto i = 0; input >> i; cout << i; // prints 6 — end example]

24.7.8.2 Class template take_while_view [range.take.while.view]

namespace std::ranges { template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> class take_while_view : public view_interface<take_while_view<V, Pred>> { // [range.take.while.sentinel], class template take_while_view::sentinel template<bool> class sentinel; // exposition only V base_ = V(); // exposition only semiregular-box<Pred> pred_; // exposition only public: take_while_view() = default; constexpr take_while_view(V base, Pred pred); constexpr V base() const& requires copy_constructible<V> { return base_; } constexpr V base() && { return std::move(base_); } constexpr const Pred& pred() const; constexpr auto begin() requires (!simple-view<V>) { return ranges::begin(base_); } constexpr auto begin() const requires range<const V> { return ranges::begin(base_); } constexpr auto end() requires (!simple-view<V>) { return sentinel<false>(ranges::end(base_), addressof(*pred_)); } constexpr auto end() const requires range<const V> { return sentinel<true>(ranges::end(base_), addressof(*pred_)); } }; template<class R, class Pred> take_while_view(R&&, Pred) -> take_while_view<views::all_t<R>, Pred>; }

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constexpr take_while_view(V base, Pred pred);

Effects: Initializes base_ with std::move(base) and pred_ with std::move(pred).

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constexpr const Pred& pred() const;

Effects: Equivalent to: return *pred_;

24.7.8.3 Class template take_while_view::sentinel [range.take.while.sentinel]

namespace std::ranges { template<view V, class Pred> requires input_range<V> && is_object_v<Pred> && indirect_unary_predicate<const Pred, iterator_t<V>> template<bool Const> class take_while_view<V, Pred>::sentinel { // exposition only using Base = conditional_t<Const, const V, V>; // exposition only sentinel_t<Base> end_ = sentinel_t<Base>(); // exposition only const Pred* pred_ = nullptr; // exposition only public: sentinel() = default; constexpr explicit sentinel(sentinel_t<Base> end, const Pred* pred); constexpr sentinel(sentinel<!Const> s) requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>; constexpr sentinel_t<Base> base() const { return end_; } friend constexpr bool operator==(const iterator_t<Base>& x, const sentinel& y); }; }

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constexpr explicit sentinel(sentinel_t<Base> end, const Pred* pred);

Effects: Initializes end_ with end and pred_ with pred.

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constexpr sentinel(sentinel<!Const> s)
  requires Const && convertible_to<sentinel_t<V>, sentinel_t<Base>>;

Effects: Initializes end_ with s.end_ and pred_ with s.pred_.

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friend constexpr bool operator==(const iterator_t<Base>& x, const sentinel& y);

Effects: Equivalent to: return y.end_ == x || !invoke(*y.pred_, *x);