std::ranges::views::take,std::ranges::take_view(3)

NAME
std::ranges::views::take,std::ranges::take_view - std::ranges::views::take,std::ranges::take_view

Synopsis
   Defined in header <ranges>
   template< ranges::view V >
   class take_view (1) (since C++20)
       : public ranges::view_interface<take_view<V>>
   namespace views {
       inline constexpr /* unspecified */ take = /* unspecified */; (2) (since C++20)
   }
   Call signature
   template< ranges::viewable_range R >
       requires /* see below */ (since C++20)
   constexpr ranges::view auto
       take( R&& r, ranges::range_difference_t<R> count );
   template< class DifferenceType >
   constexpr /* range adaptor closure */ take( DifferenceType&& count (since C++20)
   );
   1) A range adaptor that represents view of the elements from an underlying sequence,
   starting at the beginning and ending at a given bound.
   2) views::take is a RangeAdaptorObject. The expression views::take(e, f) results in
   a view that represents the first f elements from e. The result is not necessarily a
   take_view.
   views::take(e, f) is expression-equivalent to (where T is
   std::remove_cvref_t<decltype((e))> and D is
   ranges::range_difference_t<decltype((e))>):
     * ((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the
       evaluations of e and f are indeterminately sequenced;
     * U(ranges::begin(e), ranges::begin(e) + std::min<D>(ranges::distance(e), f)), if
       T is a specialization of std::span, std::basic_string_view, or ranges::subrange
       that models both random_access_range and sized_range, where U is
     * std::span<typename T::element_type>, if T is a specialization of std::span;
     * T, if T is a specialization of std::basic_string_view;
     * ranges::subrange<ranges::iterator_t<T>>, if T is a specialization of
       ranges::subrange;
     * ranges::iota_view(*ranges::begin(e),
                        *(ranges::begin(e) + std::min<D>(ranges::distance(e), f))), if
       T is a specialization of ranges::iota_view that models both random_access_range
       and sized_range;
     * otherwise, if T is a specialization of ranges::repeat_view:
     * views::repeat(*e.value_, std::min<D>(ranges::distance(e), f)), if (since C++23)
       T models sized_range; is such case e is evaluated only once;
     * views::repeat(*e.value_, static_cast<D>(e)) otherwise;
     * otherwise, take_view(e, f).
   In all cases, decltype((f)) must model std::convertible_to<D>.
   take_view models the concepts contiguous_range, random_access_range,
   bidirectional_range, forward_range, input_range, and sized_range when the underlying
   view V models respective concepts. It models common_range when the underlying view V
   models both random_access_range and sized_range.

Member functions
   constructor constructs a take_view
   (C++20) (public member function)
   base returns a copy of the underlying (adapted) view
   (C++20) (public member function)
   begin returns an iterator to the beginning
   (C++20) (public member function)
   end returns an iterator or a sentinel to the end
   (C++20) (public member function)
   size returns the number of elements. Provided only if the underlying
   (C++20) (adapted) range satisfies sized_range.
                 (public member function)
         Inherited from std::ranges::view_interface
   empty returns whether the derived view is empty. Provided if it satisfies
   (C++20) sized_range or forward_range.
                 (public member function of std::ranges::view_interface<D>)
   cbegin returns a constant iterator to the beginning of the range.
   (C++23) (public member function of std::ranges::view_interface<D>)
   cend returns a sentinel for the constant iterator of the range.
   (C++23) (public member function of std::ranges::view_interface<D>)
   operator bool returns whether the derived view is not empty. Provided if
   (C++20) ranges::empty is applicable to it.
                 (public member function of std::ranges::view_interface<D>)
   data gets the address of derived view's data. Provided if its iterator type
   (C++20) satisfies contiguous_iterator.
                 (public member function of std::ranges::view_interface<D>)
   front returns the first element in the derived view. Provided if it
   (C++20) satisfies forward_range.
                 (public member function of std::ranges::view_interface<D>)
   back returns the last element in the derived view. Provided if it satisfies
   (C++20) bidirectional_range and common_range.
                 (public member function of std::ranges::view_interface<D>)
   operator[] returns the n^th element in the derived view. Provided if it satisfies
   (C++20) random_access_range.
                 (public member function of std::ranges::view_interface<D>)
   Deduction guides
   Nested classes
   sentinel the sentinel type
   (C++20) (exposition-only member class template*)
   Helper templates
   template< class T >
   inline constexpr bool (since C++20)
   enable_borrowed_range<std::ranges::take_view<T>> =
       std::ranges::enable_borrowed_range<T>;
   This specialization of std::ranges::enable_borrowed_range makes take_view satisfy
   borrowed_range when the underlying view satisfies it.

Example
// Run this code
 #include <algorithm>
 #include <iostream>
 #include <ranges>
 auto print = [](char x){ std::cout << x; };
 int main()
 {
     constexpr char pi[]{'3', '.', '1', '4', '1', '5', '9', '2'};
     std::ranges::for_each(pi | std::ranges::views::take(6), print);
     std::cout << '\n';
     // safely takes 8 chars only, i.e. min(pi.size(), 42)
     std::ranges::for_each(std::ranges::take_view{pi, 42}, print);
     std::cout << '\n';
 }

Output:
 3.1415
 3.141592
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       views::take sometimes failed
   LWG 3407 C++20 to the result type is adjusted so
                       construct a sized random that construction is always valid
                       access range
   LWG 3494 C++20 take_view was never a it is a borrowed_range if its
                       borrowed_range underlying view is

See also
   views::counted creates a subrange from an iterator and a count
   (C++20) (customization point object)
   ranges::take_while_view a view consisting of the initial elements of another view,
   views::take_while until the first element on which a predicate returns false
   (C++20) (class template) (range adaptor object)
   ranges::copy_n copies a number of elements to a new location
   (C++20) (niebloid)