std::common...r::operator=(3)

💖 std::common...r::operator=(3) 💖

okay bestie, welcome to std::common...r::operator=(3) from the C++ Standard Libary manual — yes, “Libary” is exactly how it’s spelled on the page, don’t come for me. This is the assignment operator page, and it’s lowkey all about copying the underlying variant from another common_iterator and living your truth. 💅

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🎀 NAME 🎀

• std::common_iterator::operator= — std::common_iterator::operator=

(okay the NAME line literally says the same thing twice, and honestly? iconic. we keep it.)

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✨ Synopsis ✨

Here’s the synopsis, copied exactly because compilers are not gonna vibe with your creative rewrites:

          template< class I2, class S2 >

          requires std::convertible_to<const I2&, I> &&
                   std::convertible_to<const S2&, S> &&
                   std::assignable_from<I&, const I2&> &&
       (since C++20)
                   std::assignable_from<S&, const S2&>

          constexpr common_iterator& operator=( const common_iterator<I2, S2>&
          x );

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

Let i be 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.

🚨 undefined behavior alert 🚨 — the behavior is undefined if x is in an invalid state, that is, x.var.valueless_by_exception() is equal to true. bestie do not do this. 💀

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🍓 Parameters 🍓

• x — iterator adaptor to assign from

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🌸 Return value 🌸

*this — that’s it, that’s the return. 🫶

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🦋 Example 🦋

Run this code (the page literally says // Run this code, so we’re keeping the energy):

        #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';
        }

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🌈 Output 🌈

2 3 4 5 6
3 4 5 6

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🩹 Defect reports 🩹

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• LWG 3574 — applied to: C++20. behavior as published: variant was fully constexpr (P2231R1) but common_iterator was not. corrected behavior: common_iterator was also made constexpr. retroactive glow-up, we love to see it. 🔥

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👀 See also 👀

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

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mwah 💋 — source: http://cppreference.com, version/date: 2024.06.10, page: std::common...r::operator=(3). bye bestie, go assign responsibly 🫶✨