25 Ranges library [ranges]

25.7 Range adaptors [range.adaptors]

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.

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 modelconvertible_to,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 modelsrandom_access_range and sized_range and is a specialization ofspan ([views.span]),basic_string_view ([string.view]), orsubrange ([range.subrange]), thenU(ranges::begin(E), ranges::begin(E) + std::min(ranges::distance(E), F)), except that E is evaluated only once, where U is a type determined as follows:
- (2.2.1)

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>;

(2.3)

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(ranges::distance(E), F))), except that E is 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, thenviews::repeat(*E.value_, std::min(ranges::distance(E), F)) except that E is evaluated only once;

otherwise, views::repeat(*E.value_, static_cast(F)).

[Example 1: vector 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 â end example]