std::ranges::views::drop,std::ranges::drop_view(3)

NAME
std::ranges::views::drop,std::ranges::drop_view - std::ranges::views::drop,std::ranges::drop_view

Synopsis
   Defined in header <ranges>
   template< ranges::view V >
   class drop_view (1) (since C++20)
       : public ranges::view_interface<drop_view<V>>
   namespace views {
       inline constexpr /* unspecified */ drop = /* unspecified */; (2) (since C++20)
   }
   Call signature
   template< ranges::viewable_range R >
       requires /* see below */ (since C++20)
   constexpr ranges::view auto
       drop( R&& r, ranges::range_difference_t<R> count );
   template< class DifferenceType >
   constexpr /* range adaptor closure */ drop( DifferenceType&& count (since C++20)
   );
   1) A range adaptor consisting of elements of the underlying sequence, skipping the
   first N elements.
   2) RangeAdaptorObject. Given T is std::remove_cvref_t<decltype((e))> and D is
   ranges::range_difference_t<decltype((e))>), the expression views::drop(e, f) is
   expression-equivalent to:
     * ((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the
       evaluations of e and f are indeterminately sequenced;
     * otherwise, T(ranges::begin(e) + inc, ranges::end(e),
         /* to-unsigned-like */(ranges::distance(e) - inc)), if T is a specialization
       of ranges::subrange that models both random_access_range and sized_range, and T
       needs to store the size (see ranges::subrange::subrange for details), where inc
       is std::min<D>(ranges::distance(e), f);
     * otherwise, U(ranges::begin(e) + inc, ranges::end(e)), if T is a specialization
       of std::span, std::basic_string_view, ranges::iota_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 otherwise;
     * otherwise, if T is a specialization of ranges::repeat_view:
     * views::repeat(*e.value_, ranges::distance(e) - inc), if T models (since C++23)
       sized_range; in such case e is evaluated only once;
     * ((void)e, auto(f)) otherwise, except that the evaluations of e and
       f are indeterminately sequenced;
     * otherwise, drop_view(e, f).
   In all cases, decltype((f)) must model std::convertible_to<D>.
   drop_view models the concepts contiguous_range, random_access_range,
   bidirectional_range, forward_range, input_range, common_range, and sized_range when
   the underlying view V models respective concepts.

Member functions
   constructor constructs a drop_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
   Helper templates
   template<class T>
   inline constexpr bool (since C++20)
   enable_borrowed_range<std::ranges::drop_view<T>> =
       std::ranges::enable_borrowed_range<T>;
   This specialization of std::ranges::enable_borrowed_range makes drop_view satisfy
   borrowed_range when the underlying view satisfies it.

Example
// Run this code
 #include <iostream>
 #include <ranges>
 int main()
 {
     const auto nums = {1, 2, 3, 4, 5, 6, 7};
     std::cout << "drop " << 2 << ": ";
     for (int i : std::ranges::drop_view{nums, 2})
         std::cout << i << ' ';
     std::cout << '\n';
     std::cout << "drop " << 3 << ": ";
     for (int i : nums | std::views::drop(3))
         std::cout << i << ' ';
     std::cout << '\n';
     std::cout << "drop " << 4 << ": ";
     for (int i : std::views::iota(1, 8) | std::views::drop(4))
         std::cout << i << ' ';
     std::cout << '\n';
     // Note that dropping more than the number of elements is OK:
     for (int dp : {5, 6, 7, 890, 100500})
     {
         std::cout << "drop " << dp << ": ";
         for (int i : std::views::iota(1, 8) | std::views::drop(dp))
             std::cout << i << ' ';
         std::cout << '\n';
     }
 }

Output:
 drop 2: 3 4 5 6 7
 drop 3: 4 5 6 7
 drop 4: 5 6 7
 drop 5: 6 7
 drop 6: 7
 drop 7:
 drop 890:
 drop 100500:
   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::drop sometimes fails to the construction is adjusted
   LWG 3407 C++20 construct a sized random so that it is always valid
                       access range
   LWG 3494 C++20 drop_view was never a it is a borrowed_range if its
                       borrowed_range underlying view is

See also
   ranges::drop_while_view a view consisting of the elements of another view, skipping
   views::drop_while the initial subsequence of elements until the first element
   (C++20) where the predicate returns false
                        (class template) (range adaptor object)