25 Ranges library [ranges]

drop_view produces a view excluding the first N elements from another view, or an empty range if the adapted view contains fewer than N elements.

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

Let E and F be expressions, let T be remove_cvref_t<decltype((E))>, and let D be range_difference_t<decltype((E))>.

If decltype((F)) does not model convertible_to<D>, views​::​drop(E, F) is ill-formed.

Otherwise, the expression views​::​drop(E, F) is expression-equivalent to:

• (2.1)
  If T is a specialization of empty_view ([range.empty.view]), then ((void)F, decay-copy(E)), except that the evaluations of E and F are indeterminately sequenced.
• (2.2)
  Otherwise, if T models random_access_range and sized_range and is

  • (2.2.1)
    a specialization of span ([views.span]),
  • (2.2.2)
    a specialization of basic_string_view ([string.view]),
  • (2.2.3)
    a specialization of iota_view ([range.iota.view]), or
  • (2.2.4)
    a specialization of subrange ([range.subrange]) where T​::​StoreSize is false,

  then U(ranges​::​begin(E) + std​::​min<D>(ranges​::​distance(E), F), ranges​::​end(E)), except that E is evaluated only once, where U is span<typename T​::​element_type> if T is a specialization of span and T otherwise.
• (2.3)
  Otherwise, if T is a specialization of subrange that models random_access_range and sized_range, then T(ranges​::​begin(E) + std​::​min<D>(ranges​::​distance(E), F), ranges​::​end(E), to-unsigned-like(ranges​::​distance(E) - std​::​min<D>(ranges​::​distance(E), F))), except that E and F are each evaluated only once.
• (2.4)
  Otherwise, if T is a specialization of repeat_view ([range.repeat.view]):

  • (2.4.1)
    if T models sized_range, then views::repeat(*E.value_, ranges::distance(E) - std::min<D>(ranges::distance(E), F)) except that E is evaluated only once;
  • (2.4.2)
    otherwise, ((void)F, decay-copy(E)), except that the evaluations of E and F are indeterminately sequenced.
• (2.5)
  Otherwise, drop_view(E, F).