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

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< cpp‎ | iterator‎ | common iterator

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:

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

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

### Parameters

x | - | iterator adaptor to assign from

### Return value

*this.

### Example

Run this code

    #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<
                       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';
    }

Output:

    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

(constructor) (C++20) | constructs a new iterator adaptor (public member function)

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