std::common_reference_with(3)

🦋 std::common_reference_with(3) 🦋

okay bestie, welcome to the C++ Standard Libary manual page for std::common_reference_with — yes, the header spells it “Libary”, and we’re keeping the vibe intact 💅. This is the page about the concept that says two types share a common reference type (as computed by std::common_reference_t) that both can convert to. Periodt. ✨

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🎀 NAME 🎀

std::common_reference_with — literally std::common_reference_with, bestie. That’s the name. No cap. 💖

🌸 Synopsis 🌸

Defined in header <concepts>:

template< class T, class U >

concept common_reference_with =
    std::same_as<std::common_reference_t<T, U>,
                 std::common_reference_t<U, T>> &&
    std::convertible_to<T, std::common_reference_t<T, U>> &&

    std::convertible_to<U, std::common_reference_t<T, U>>;

(since C++20) — this concept is giving main character energy 🔥.

The concept common_reference_with<T, U> specifies that two types T and U share a common reference type (as computed by std::common_reference_t) to which both can be converted. 🫶

🧠 Semantic requirements 🧠

T and U model std::common_reference_with<T, U> only if, given equality-preserving expressions t1, t2, u1 and u2 such that decltype((t1)) and decltype((t2)) are both T and decltype((u1)) and decltype((u2)) are both U,

• std::common_reference_t<T, U>(t1) equals std::common_reference_t<T, U>(t2) if and only if t1 equals t2; and
• std::common_reference_t<T, U>(u1) equals std::common_reference_t<T, U>(u2) if and only if u1 equals u2.

In other words, the conversion to the common reference type must preserve equality. That’s the whole vibe check: equality has to survive the conversion, bestie. 😭💖

👀 See also 👀

• common_reference — determines the common reference type of a group of types
• basic_common_reference — (class template) (C++20)
• common_with — specifies that two types share a common type; (C++20) (concept)
• common_type — determines the common type of a group of types; (C++11) (class template)

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mwah 💋 — source http://cppreference.com, version/date 2024.06.10, page std::common_reference_with(3). Slay, and happy concept-ing 🧚✨