std::experi...onReference(3)

Okay bestie, this page is from the C++ Standard Libary manual — yes, that's the manual name, typo and all — and the page is std::experimental::ranges::CommonReference / std::experi...onReference(3). It's a ranges TS concept, and it's lowkey iconic. 💅

💖 NAME 💖

std::experimental::ranges::CommonReference — std::experimental::ranges::CommonReference.

Periodt. That's the name and also the name again, because manpages love a little repetition. 🎀

✨ Synopsis ✨

First up, bestie: it's Defined in header <experimental/ranges/concepts>.

Then the synopsis hits you with:

template< class T, class U >

concept bool CommonReference =
    Same<ranges::common_reference_t<T, U>,
(ranges TS)
    ranges::common_reference_t<U, T>> &&
    ConvertibleTo<T, ranges::common_reference_t<T, U>> &&

    ConvertibleTo<U, ranges::common_reference_t<T, U>>;

And yes, (ranges TS) is literally sitting in there in the original synopsis — I'm keeping the details exactly, bestie. No cap. 🫶

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

CommonReference<T, U> is satisfied only if, given expressions t and u such that decltype((t)) is T and decltype((u)) is U:

• ranges::common_reference_t<T, U>(t) is equal to ranges::common_reference_t<T, U>(t) if and only if t is an equality-preserving expression; and
• ranges::common_reference_t<T, U>(u) is equal to ranges::common_reference_t<T, U>(u) if and only if u is an equality-preserving expression.

In other words, the conversion to the common reference type must not alter the equality-preservation property of the original expression. It's giving "don't change the vibe of the original expression." 💜

🌸 Equality preservation 🌸

An expression is equality preserving if it results in equal outputs given equal inputs.

• The inputs to an expression consist of its operands.
• The outputs of an expression consist of its result and all operands modified by the expression (if any).

Every expression required to be equality preserving is further required to be stable: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.

Bestie, this is the important part: equality preservation is not just a cute word. It's a real requirement, and stability is tagging along with it. 👑

👀 See also 👀

• common_reference — determine the common reference type of a set of types (class template)
• Common — specifies that two types share a common type (concept)
• common_type — determine the common type of a set of types (class template)

Source: http://cppreference.com · version/date: 2024.06.10 · page: std::experi...onReference(3). Bye bestie, go be equality-preserving and stable out there 💅✨🎀