User:T. Canens/ranges notes

• Qualification style: ranges::foo and std::foo.
  • Exception: for something in std, spell out the full std::experimental::ranges::foo
• Decide on where/how to decompose complex concepts (Sortable being an example):
  • Template transcluded on each algorithm page using it?
  • Note on the concept's page?
  • Goal: A user shouldn't have to click on more than a couple of links to figure out what T has to satisfy in order to use ranges::sort on a std::vector<T>.
• Cover [concepts.lib.general.equality] somewhere.
  • Key points: equality preservation; which inputs may be modified; implicit expression variants
  • Decide how to cover them.
    • Template and transclude on every concept page that is relevant?
    • Dedicated section + links?
• Algorithms.
  • May need a template for the "return the past-the-end iterator of the range" thing.
  • Document various caveats in remarks? (But note https://github.com/ericniebler/stl2/issues/261)

• No intended difference between R(&f)() and use f() vs. "f be an expression such that decltype((f)) is R" and use f. But need to watch out for possible missing "equality-preserving". See issues #531 and #532

implicit expression variations

• Casey: "implicit expression variations" applies to all id-expressions that are const lvalues (after substitution)
  • Non-id-expressions not included
  • Remember to check while writing if it's sane
• Casey: intended that ranges::Assignable<T&, const T&> spawn variations for the expression in

requires(T t, U&& u) {
    { t = std::forward<U>(u) } -> ranges::Same<T>&&;
  }

, treating the whole std::forward<U>(u) as the "operand" (not just the id-expression u, contrary to previous note)

• Casey: This is needed for Copyable.
• Casey: standalone ranges::Assignable<T&, const T&> requires all implicit variations on the assignment expression to be non-modifying for the right operand (including when it's a non-const rvalue), but ranges::Copyable<T> removes that requirement because it also requires ranges::Movable which requires ranges::Assignable<T&, T>, which counts as an explicit requirement that supersedes the implicit requirement.
  • i.e., the same concept-id can mean different things depending on whether it is used stand-alone or as part of another concept. Explicit/implicit superseding can happen "at a distance" and isn't local to a concept.