std::common_iterator<I,S>::operator=

 

C++

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迭代器概念
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
迭代器原语
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (C++17 中弃用) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
算法概念与工具
间接可调用概念
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
常用算法要求
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
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indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
迭代器适配器
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
流迭代器 istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	迭代器定制点 ranges::iter_move (C++20) ranges::iter_swap (C++20)
迭代器操作 advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	范围访问 begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

std::common_iterator

成员函数

common_iterator::common_iterator

common_iterator::operator=

common_iterator::operator*common_iterator::operator->

common_iterator::operator++common_iterator::operator++(int)

非成员函数

operator== (C++20)

operator- (C++20)

iter_move (C++20)

iter_swap (C++20)

辅助类

incrementable_traits<std::common_iterator> (C++20)

iterator_traits<std::common_iterator> (C++20)

 

template< class I2, class S2 > requires std::convertible_to<const I2&, I> &&          std::convertible_to<const S2&, S> &&          std::assignable_from<I&, const I2&> &&          std::assignable_from<S&, const S2&> constexpr common_iterator& operator=( const common_iterator<I2, S2>& x );		(C++20 起)

从 x 的底层 std::variant 成员对象 var 赋值给 *this 的该成员。

令 i 为 x.var.index()。则此赋值运算符等价于：

• std::get<i>(var) = std::get<i>(x.var)，若 var.index() == i，
• 否则为 var.emplace<i>(std::get<i>(x.var))。

若 x 处于无效状态，即 x.var.valueless_by_exception() 等于 true，则行为未定义。

参数

x

-

要从之赋值的迭代器适配器

返回值

*this

参数

运行此代码

#include <algorithm>
#include <initializer_list>
#include <iostream>
#include <iterator>
 
int main()
{
    const auto il = {1, 2, 3, 4, 5, 6};
    using CI = std::common_iterator<
                   std::counted_iterator<std::initializer_list<int>::iterator>,
                   std::default_sentinel_t>;
    CI first{std::counted_iterator{std::next(begin(il), 1), ssize(il) - 1}};
    const CI first2{std::counted_iterator{std::next(begin(il), 2), ssize(il) - 2}};
    const CI last{std::default_sentinel};
    std::copy(first, last, std::ostream_iterator<int>{std::cout, " "});
    std::cout << '\n';
    first = first2;
    std::copy(first, last, std::ostream_iterator<int>{std::cout, " "});
    std::cout << '\n';
}

输出：

2 3 4 5 6 
3 4 5 6

缺陷报告

下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。

缺陷报告	应用于	出版时的行为	正确行为
LWG 3574	C++20	variant 为完全 constexpr (P2231R1) 但 common_iterator 不是	亦使之为 constexpr

参阅

(构造函数) (C++20)

构造新的迭代器适配器 (公开成员函数)