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

25 Ranges library [ranges]

take_view produces a view of the first N elements from another view, or all the elements if the adapted view contains fewer than N.

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::take(E, F) is ill-formed.

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

If T is a specialization of empty_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 ofspan ([views.span]),basic_string_view ([string.view]), orsubrange ([range.subrange]), thenU(ranges::begin(E), ranges::begin(E) + std::min<D>(ranges::distance(E), F)), except that E is evaluated only once, where U is a type determined as follows:
- if T is a specialization of span, then U is span<typename T::element_type>;
- otherwise, if T is a specialization of basic_string_view, then U is T;
- otherwise, T is a specialization of subrange, andU is subrange<iterator_t<T>>;
otherwise, if T is a specialization of iota_view ([range.iota.view]) that models random_access_range and sized_range, theniota_view(*ranges::begin(E),*(ranges::begin(E) + std::min<D>(ranges::distance(E), F))), except that E is evaluated only once.
Otherwise, if T is a specialization of repeat_view ([range.repeat.view]):
- if T models sized_range, thenviews::repeat(*E.value_, std::min<D>(ranges::distance(E), F)) except that E is evaluated only once;
- otherwise, views::repeat(*E.value_, static_cast<D>(F)).
Otherwise, take_view(E, F).

[Example 1: vector<int> is{0,1,2,3,4,5,6,7,8,9};for (int i : is | views::take(5)) cout << i << ' '; — _end example_]