[range.take.overview]

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

Otherwise, the expression views::take(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 is a specialization of optional and T models view, then (static_cast<D>(F) == D() ? ((void)E, T() : decay-copy(E)).
(2.3)
Otherwise, if T models random_access_range and sized_range and is a specialization of span ([views.span]), basic_string_view ([string.view]), or subrange ([range.subrange]), then U(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:
- (2.3.1)
  if T is a specialization of span, then U is span<typename T::element_type>;
- (2.3.2)
  otherwise, if T is a specialization of basic_string_view, then U is T;
- (2.3.3)
  otherwise, T is a specialization of subrange, and U is subrange<iterator_t<T>>;
(2.4)
otherwise, if T is a specialization of iota_view ([range.iota.view]) that models random_access_range and sized_range, then iota_view(*ranges::begin(E), *(ranges::begin(E) + std::min<D>(ranges::distance(E), F)), except that E is evaluated only once.
(2.5)
Otherwise, if T is a specialization of repeat_view ([range.repeat.view]):
- (2.5.1)
  if T models sized_range, then views::repeat(*E.value_, std::min<D>(ranges::distance(E), F)) except that E is evaluated only once;
- (2.5.2)
  otherwise, views::repeat(*E.value_, static_cast<D>(F)).
(2.6)
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 << ' '; / prints 0 1 2 3 4 — end example]