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std::ranges::views::drop, std::ranges::drop_view

From cppreference.com
< cpp‎ | ranges
 
 
 
 
Defined in header <ranges>
template< ranges::view V >
class drop_view : public ranges::view_interface<drop_view<V>>
(1) (since C++20)
namespace views {

    inline constexpr /*unspecified*/ drop = /*unspecified*/;

}
(2) (since C++20)
1) A range adaptor consisting of elements of the underlying sequence, skipping the first N elements.
2) 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:
  • std::span where T::extent == std::dynamic_extent,
  • std::basic_string_view,
  • ranges::iota_view, or
  • ranges::subrange;
  • 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.

Contents

[edit] Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

[edit] Member functions

constructs a drop_view
(public member function) [edit]
(C++20)
returns a copy of the underlying (adapted) view
(public member function) [edit]
(C++20)
returns an iterator to the beginning
(public member function) [edit]
(C++20)
returns an iterator or a sentinel to the end
(public member function) [edit]
(C++20)
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range
(public member function) [edit]
Inherited from std::ranges::view_interface
(C++20)
Returns whether the derived view is empty. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
Returns whether the derived view is not empty. Provided if ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>) [edit]
(C++20)
Returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range.
(public member function of std::ranges::view_interface<D>) [edit]
Returns the nth element in the derived view. Provided if it satisfies random_access_range.
(public member function of std::ranges::view_interface<D>) [edit]

[edit] Deduction guides

[edit] Helper templates

template<class T>

inline constexpr bool enable_borrowed_range<std::ranges::drop_view<T>> =

    std::ranges::enable_borrowed_range<T>;
(since C++20)

This specialization of std::ranges::enable_borrowed_range makes drop_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Example

#include <ranges>
#include <iostream>
 
int main()
{
    const auto nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
 
    for (int i : nums | std::views::drop(2))
        std::cout << i << ' ';
    std::cout << '\n';
 
    for (int i : std::views::iota(1, 10) | std::views::drop(2))
        std::cout << i << ' ';
    std::cout << '\n';
 
    for (int i : std::ranges::drop_view{nums, 2})
        std::cout << i << ' ';
    std::cout << '\n';
}

Output:

3 4 5 6 7 8 9 
3 4 5 6 7 8 9 
3 4 5 6 7 8 9

[edit] 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 drop_view was never a borrowed_range it is a borrowed_range if its underlying view is

[edit] See also

a view consisting of the elements of another view, skipping the initial subsequence of elements until the first element where the predicate returns false
(class template) (range adaptor object) [edit]