design-roll-up-notes.md

Design changes tweaks by LWG after the Kona meeting

• stoppable_token::stop_possible() and stoppable_token::stop_requested() are now required to return precisely bool, not boolean-testable.

• The syntactic requirements for the stoppable_token have been relaxed such that an implementation is not required to check for callback constructibility from all permutations of const and &. The const& one is required and the rest become semantic constraints.

• We added a type alias stop_callback_for_t such that stop_callback_for_t<T, CB> is an alias for typename T::template callback_type<CB>.

• The bool-returning member functions of never_stop_token are made [[nodiscard]] for consistency with [[stop_token]].

• The behavior of in_place_stop_source::stop_possible() is changed to reflect the fact that an in_place_stop_source always has "ownership" of a stop state (there is no std::nostopstate_t constructor). This is for consistency with std::stop_source.

• Sender queries are moved into a separate queryable "attributes" object that is accessed by passing the sender to get_attrs(). The sender concept is reexpressed to require get_attrs() and separated from a new sender_in<Snd, Env> concept for checking whether a type is a sender within a particular execution environment.

• The placeholder types no_env and dependent_completion_signatures<> are no longer needed and are dropped.

• ensure_started and split are changed to persist the result of calling get_attrs() on the input sender.

• ask LEWG about renaming set_value_t to set_value_tag