std::ranges::views::take_while, std::ranges::take_while_view - cppreference.com (original) (raw)
std::ranges::take_while_view
| Defined in header | ||
|---|---|---|
| template< ranges::view V, class Pred > requires ranges::input_range<V> && std::is_object_v<Pred> && std::indirect_unary_predicate<const Pred, ranges::iterator_t<V>> class take_while_view : public ranges::view_interface<take_while_view<V, Pred>> | (1) | (since C++20) |
| namespace views { inline constexpr /*unspecified*/ take_while = /*unspecified*/; } | (2) | (since C++20) |
| Call signature | ||
| template< ranges::viewable_range R, class Pred > requires /* see below */ constexpr ranges::view auto take_while( R&& r, Pred&& pred ); | (since C++20) | |
| template< class Pred > constexpr /*range adaptor closure*/ take_while( Pred&& pred ); | (since C++20) |
- A range adaptor that represents view of the elements from an underlying sequence, starting at the beginning and ending at the first element for which the predicate returns false.
take_while_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, and input_range when the underlying view V models respective concepts.
Contents
[edit] Data members
| Member | Description |
|---|---|
| V base_ (private) | the underlying view(exposition-only member object*) |
| copyable-box(until C++23)movable-box(since C++23) pred_ (private) | the underlying function object(exposition-only member object*) |
[edit] Member functions
| (constructor) | constructs a take_while_view (public member function) [edit] |
|---|---|
| base | returns a copy of the underlying (adapted) view (public member function) [edit] |
| pred | returns a reference to the stored predicate (public member function) [edit] |
| begin | returns an iterator to the beginning (public member function) [edit] |
| end | returns a sentinel representing the end (public member function) [edit] |
| Inherited from std::ranges::view_interface | |
| empty | returns whether the derived view is empty, provided only if it satisfies sized_range or forward_range (public member function of std::ranges::view_interface) [edit] |
| cbegin(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface) [edit] |
| cend(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface) [edit] |
| operator bool | returns whether the derived view is not empty, provided only if ranges::empty is applicable to it (public member function of std::ranges::view_interface) [edit] |
| data | gets the address of derived view's data, provided only if its iterator type satisfies contiguous_iterator (public member function of std::ranges::view_interface) [edit] |
| front | returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface) [edit] |
| operator[] | returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface) [edit] |
[edit] Deduction guides
[edit] Nested classes
| | the sentinel type(exposition-only member class template*) | | ------------------------------------------------------------- |
[edit] Notes
For forward_iterators, views::take_while(v, pred) is similar to ranges::subrange{ranges::begin(v), ranges::find_if_not(v, pred)}, but the latter invokes pred only during construction (while the former invokes pred each time a valid take_while iterator is compared to a sentinel).
[edit] Example
#include #include int main() { for (int year : std::views::iota(2020) | std::views::take_while([](int y){ return y < 2026; })) std::cout << year << ' '; std::cout << '\n'; const char note[]{"Today is yesterday's tomorrow!..."}; auto not_dot = [](char c){ return c != '.'; }; for (char x : std::ranges::take_while_view(note, not_dot)) std::cout << x; std::cout << '\n'; }
Output:
2020 2021 2022 2023 2024 2025 Today is yesterday's tomorrow!