std::experi...es::Relation(3)

okay so this is std::experi...es::Relation(3), and we're hanging out in the C++ Standard Libary manual. yes, Libary, that's literally the spelling in the source, bestie 💅

✨ NAME ✨

std::experimental::ranges::Relation — std::experimental::ranges::Relation

short, iconic, no notes 🎀

📝 Synopsis 📝

okay so the synopsis is literally giving concept-declaration realness, and I'm obsessed:

Defined in header <experimental/ranges/concepts>
template< class R, class T, class U >

concept bool Relation =
    Predicate<R, T, T> &&
    Predicate<R, U, U> &&
    CommonReference<
        const std::remove_reference_t<T>&,
        const std::remove_reference_t<U>&> &&
    Predicate<R,                                   (1) (ranges TS)
    ranges::common_reference_t<
        const std::remove_reference_t<T>&,
        const std::remove_reference_t<U>&>,
    ranges::common_reference_t<
        const std::remove_reference_t<T>&,
        const std::remove_reference_t<U>&>> &&
    Predicate<R, T, U> &&

    Predicate<R, U, T>;

The concept Relation<R, T, U> specifies that R defines a binary relation over the set of expressions whose type and value category are those encoded by either T or U. no cap, that's the vibe 🌸

Given:

• r, an expression such that decltype((r)) is R,
• t, an expression such that decltype((t)) is T,
• u, an expression such that decltype((u)) is U,

and let C be ranges::common_reference_t<const std::remove_reference_t<T>&, const std::remove_reference_t<U>&>, then Relation<R, T, U> is satisfied only if:

• bool(r(t, u)) == bool(r(C(t), C(u))) and
• bool(r(u, t)) == bool(r(C(u), C(t))).

that's the whole condition, bestie — both of those bool comparisons have to line up, periodt 🔥

okay bye bestie 🫶 this page came from http://cppreference.com, dated 2024.06.10, and the title on it is std::experi...es::Relation(3).