std::ranges::borrowed_iterator_t, std::ranges::borrowed_subrange_t

 

C++

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技术规范

 

范围库

范围访问
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
范围原语
iterator_tsentinel_t	range_size_trange_difference_t	range_reference_trange_rvalue_reference_t	range_value_t
悬垂迭代器处理
dangling	borrowed_iterator_t	borrowed_subrange_t
范围概念
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
视图
view_interface	subrange
范围工厂
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	basic_istream_viewviews::istream
适配器
views::all_tviews::all ref_view owning_view common_viewviews::common reverse_viewviews::reverse views::counted zip_viewviews::zip (C++23)(C++23)	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while zip_transform_viewviews::zip_transform (C++23)(C++23)	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform adjacent_viewviews::adjacent (C++23)(C++23)	filter_viewviews::filter join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)
范围适配器对象
范围适配器闭包对象
辅助项
copyable-box	simple-view

 

定义于头文件 <ranges>
template< ranges::range R > using borrowed_iterator_t = /* see below */;	(1)	(C++20 起)
template< ranges::range R > using borrowed_subrange_t = /* see below */;	(2)	(C++20 起)

1) 若 R 实现 borrowed_range 则为 std::ranges::iterator_t<R> ，否则为 std::ranges::dangling 。

2) 若 R 实现 borrowed_range 则为 std::ranges::subrange<std::ranges::iterator_t<R>> ，否则为 std::ranges::dangling 。

某些受约束算法用此二模板别名避免返回潜在悬垂的迭代器或视图。

可能的实现

版本一
template< std::ranges::range R > using borrowed_iterator_t = std::conditional_t<std::ranges::borrowed_range<R>, std::ranges::iterator_t<R>, std::ranges::dangling>;
版本二
template< std::ranges::range R > using borrowed_subrange_t = std::conditional_t<std::ranges::borrowed_range<R>, std::ranges::subrange<std::ranges::iterator_t<R>>, std::ranges::dangling>;

参阅

ranges::dangling (C++20)

占位类型，指示不应返回迭代器或子范围，因为它可能悬垂 (类)