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 > (1) (since C++20)
   class take_view : 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, class DifferenceType >
   requires /* see below */ (since C++20)
   constexpr ranges::view auto take( R&& r, DifferenceType&& 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 range adaptor object. 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.
   It is expression-equivalent to (where T is std::remove_cvref_t<decltype((e))> and D
   is ranges::range_difference_t<decltype((e))>):
     * ((void)f, static_cast<T>(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, 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.
  Expression-equivalent
   Expression e is expression-equivalent to expression f, if
     * e and f have the same effects, and
     * either both are constant subexpressions or else neither is a constant
       subexpression, and
     * either both are potentially-throwing or else neither is potentially-throwing
       (i.e. noexcept(e) == noexcept(f)).

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>)
   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 nth 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';
     std::ranges::for_each(std::ranges::take_view{pi, 42}, print); // safely takes only 8 chars
     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
   LWG 3494 C++20 take_view was never a it is a borrowed_range if its
                       borrowed_range underlying view is
                       views::take sometimes fails the result type is adjusted so that
   LWG 3407 C++20 to construct construction is always valid
                       a sized random access range

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)