[range.drop.overview] (original) (raw)

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.

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 modelconvertible_to<D>,views::drop(E, F) is ill-formed.

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

If T is a specialization ofempty_view ([range.empty.view]), then ((void)F, decay-copy(E)), except that the evaluations of E and Fare indeterminately sequenced.
Otherwise, if T modelsrandom_access_range and sized_rangeand is
- a specialization of span ([views.span]),
- a specialization of basic_string_view ([string.view]),
- a specialization of iota_view ([range.iota.view]), or
- 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.
Otherwise, if T is a specialization of subrangethat models random_access_range and sized_range, thenT(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.
Otherwise, if T is a specialization of repeat_view ([range.repeat.view]):
- if T models sized_range, thenviews::repeat(*E.value_, ranges::distance(E) - std::min<D>(ranges::distance(E), F)) except that E is evaluated only once;
- otherwise, ((void)F, decay-copy(E)), except that the evaluations of E and F are indeterminately sequenced.
Otherwise, drop_view(E, F).

[Example 1: auto ints = views::iota(0) | views::take(10);for (auto i : ints | views::drop(5)) { cout << i << ' '; } — _end example_]