24 Ranges library [ranges]

24.7 Range adaptors [range.adaptors]

24.7.13 Common view [range.common]

24.7.13.2 Class template common_­view [range.common.view]

namespace std::ranges {
  template<view V>
    requires (!common_range<V>)
  class common_view : public view_interface<common_view<V>> {
  private:
    V base_ = V();  // exposition only
  public:
    common_view() = default;

    constexpr explicit common_view(V r);

    template<viewable_range R>
      requires (!common_range<R> && constructible_from<V, all_view<R>>)
    constexpr explicit common_view(R&& r);

    constexpr V base() const;

    constexpr auto size() requires sized_range<V> {
      return ranges::size(base_);
    }
    constexpr auto size() const requires sized_range<const V> {
      return ranges::size(base_);
    }

    constexpr auto begin() {
      if constexpr (random_access_range<V> && sized_range<V>)
        return ranges::begin(base_);
      else
        return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::begin(base_));
    }

    constexpr auto begin() const requires range<const V> {
      if constexpr (random_access_range<const V> && sized_range<const V>)
        return ranges::begin(base_);
      else
        return common_iterator<iterator_t<const V>, sentinel_t<const V>>(ranges::begin(base_));
    }

    constexpr auto end() {
      if constexpr (random_access_range<V> && sized_range<V>)
        return ranges::begin(base_) + ranges::size(base_);
      else
        return common_iterator<iterator_t<V>, sentinel_t<V>>(ranges::end(base_));
    }

    constexpr auto end() const requires range<const V> {
      if constexpr (random_access_range<const V> && sized_range<const V>)
        return ranges::begin(base_) + ranges::size(base_);
      else
        return common_iterator<iterator_t<const V>, sentinel_t<const V>>(ranges::end(base_));
    }
  };

  template<class R>
    common_view(R&&) -> common_view<all_view<R>>;
}
constexpr explicit common_view(V base);
Effects: Initializes base_­ with std​::​move(base).
template<viewable_range R> requires (!common_range<R> && constructible_from<V, all_view<R>>) constexpr explicit common_view(R&& r);
Effects: Initializes base_­ with views​::​all(std​::​forward<R>(r)).
constexpr V base() const;
Effects: Equivalent to: return base_­;