namespace std::ranges {
template<input_range V, indirect_unary_predicate<iterator_t<V>> Pred>
requires view<V> && is_object_v<Pred>
class filter_view : public view_interface<filter_view<V, Pred>> {
private:
V base_ = V();
semiregular-box<Pred> pred_;
class iterator;
class sentinel;
public:
filter_view() = default;
constexpr filter_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 iterator begin();
constexpr auto end() {
if constexpr (common_range<V>)
return iterator{*this, ranges::end(base_)};
else
return sentinel{*this};
}
};
template<class R, class Pred>
filter_view(R&&, Pred) -> filter_view<views::all_t<R>, Pred>;
}
constexpr filter_view(V base, Pred pred);
Effects:
Initializes
base_ with
std::move(base) and initializes
pred_ with
std::move(pred). constexpr const Pred& pred() const;
Effects:
Equivalent to: return *pred_;
constexpr iterator begin();
Preconditions:
pred_.has_value(). Returns:
{*this, ranges::find_if(base_, ref(*pred_))}. Remarks:
In order to provide the amortized constant time complexity required by
the
range concept
when
filter_view models
forward_range,
this function caches the result within the
filter_view for use on subsequent calls
.