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std::common_iterator<I,S>::operator= - cppreference.com

From cppreference.com

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 );
(since C++20)

Assigns the underlying std::variant member object var from that of x.

Let Ix be x.var .index(). Then, this assignment is equivalent to:

  • std::get<Ix>(var ) = std::get<Ix>(x.var ), if var.index() == Ix,
  • var .emplace<Ix>(std::get<Ix>(x.var )) otherwise.

If x.var .valueless_by_exception() is true (i.e. x is in an invalid state), the behavior is undefined.

(until C++26)

If x.var .valueless_by_exception() is true (i.e. x is in an invalid state):

(since C++26)

Parameters

x - iterator adaptor to assign from

Return value

*this

Example

#include <algorithm>
#include <initializer_list>
#include <iostream>
#include <iterator>

int main()
{
    const auto il = {1, 2, 3, 4, 5, 6};
    
    using LI = std::initializer_list<int>::iterator;
    using CI = std::common_iterator<std::counted_iterator<LI>,
                                    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';
}

Output:

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 3574 C++20 variant was fully constexpr (P2231R1) but common_iterator was not also made constexpr

See also