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Defined in header <ranges> | ||
template<ranges::view V> class drop_view | (1) | (since C++20) |
namespace views{ inlineconstexpr/* unspecified */ drop=/* unspecified */; | (2) | (since C++20) |
Call signature | ||
template<ranges::viewable_range R> requires/* see below */ | (since C++20) | |
template<class DifferenceType> constexpr/* range adaptor closure */ drop( DifferenceType&& count); | (since C++20) | |
T isstd::remove_cvref_t<decltype((e))> andD isranges::range_difference_t<decltype((e))>), the expressionviews::drop(e, f) isexpression-equivalent to: decay-copy(e)), ifT is aranges::empty_view, except that the evaluations ofe andf are indeterminately sequenced;T is a specialization ofranges::subrange that models bothrandom_access_range andsized_range, andT needs to store the size (seeranges::subrange::subrange() for details), whereinc isstd::min<D>(ranges::distance(e), f);T is a specialization ofstd::span,std::basic_string_view,ranges::iota_view, orranges::subrange that models bothrandom_access_range andsized_range, whereU is
| (since C++23) |
drop_view models the conceptscontiguous_range,random_access_range,bidirectional_range,forward_range,input_range,common_range, andsized_range when the underlying viewV models respective concepts.
Contents |
| Member | Description |
Vbase_(private) | the underlying view (exposition-only member object*) |
ranges::range_difference_t<V>count_(private) | the number of elements to skip (exposition-only member object*) |
non-propagating-cache<ranges::iterator_t<V>>cache_(private)(present only if V satisfiesforward_range but notrandom_access_range andsized_range) | an object that caches the result of calls tobegin()(exposition-only member object*) |
constructs adrop_view(public member function)[edit] | |
| returns a copy of the underlying (adapted) view (public member function)[edit] | |
| returns an iterator to the beginning (public member function)[edit] | |
| returns an iterator or a sentinel to the end (public member function)[edit] | |
returns the number of elements, provided only if the underlying (adapted) range satisfiessized_range(public member function)[edit] | |
(C++26) | returns the approximate size of the resultingapproximately_sized_range(public member function)[edit] |
Inherited fromstd::ranges::view_interface | |
returns whether the derived view is empty, provided only if it satisfiessized_range orforward_range(public member function of std::ranges::view_interface<D>)[edit] | |
(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface<D>)[edit] |
(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface<D>)[edit] |
| returns whether the derived view is not empty, provided only ifranges::empty is applicable to it (public member function of std::ranges::view_interface<D>)[edit] | |
gets the address of derived view's data, provided only if its iterator type satisfiescontiguous_iterator(public member function of std::ranges::view_interface<D>)[edit] | |
returns the first element in the derived view, provided if it satisfiesforward_range(public member function of std::ranges::view_interface<D>)[edit] | |
returns the last element in the derived view, provided only if it satisfiesbidirectional_range andcommon_range(public member function of std::ranges::view_interface<D>)[edit] | |
returns thenth element in the derived view, provided only if it satisfiesrandom_access_range(public member function of std::ranges::view_interface<D>)[edit] | |
template<class T> constexprbool enable_borrowed_range<std::ranges::drop_view<T>>= | (since C++20) | |
This specialization ofranges::enable_borrowed_range makesdrop_view satisfyborrowed_range when the underlying view satisfies it.
#include <initializer_list>#include <iostream>#include <ranges> int main(){constauto 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 7drop 3: 4 5 6 7drop 4: 5 6 7drop 5: 6 7drop 6: 7drop 7:drop 890: drop 100500:
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3407 | C++20 | views::drop sometimes fails toconstruct a sized random access range | the construction is adjusted so that it is always valid |
| LWG 3494 | C++20 | drop_view was never aborrowed_range | it is aborrowed_range if its underlying view is |
aview consisting of the elements of anotherview, skipping the initial subsequence of elements until the first element where the predicate returnsfalse(class template)(range adaptor object)[edit] |
