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 i is x.var.index(). Then, this assignment is equivalent to:

The behavior is undefined if x is in an invalid state, that is, x.var.valueless_by_exception() is equal to true.


x - iterator adaptor to assign from

Return value



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


2 3 4 5 6 
3 4 5 6

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

constructs a new iterator adaptor
(public member function)

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