Proposed resolution:

This wording is relative to N5001.

1. Change [exec.snd.concepts] as indicated:

   
     template<class Sndr>
       concept is-sender =                                         // exposition only
         derived_from<typename Sndr::sender_concept, sender_t>;
   
     template<class Sndr>
       concept enable-sender =                                     // exposition only
         is-sender<Sndr> ||
         is-awaitable<Sndr, env-promise<empty_env>>;               // [exec.awaitable]
   
     template<class Sndr>
       inline constexpr bool enable_sender = enable-sender<Sndr>;
   
     template<class Sndr>
       concept sender =
         bool(enable-senderenable_sender<remove_cvref_t<Sndr>>) &&
         requires (const remove_cvref_t<Sndr>& sndr) {
           { get_env(sndr) } -> queryable;
         } &&
         move_constructible<remove_cvref_t<Sndr>> &&
         constructible_from<remove_cvref_t<Sndr>, Sndr>;
   

   …

   -2- Given a subexpression `sndr`, […]

   -?- Remarks: Pursuant to [namespace.std], users may specialize `enable_sender` to `true` for cv-unqualified program-defined types that model `sender`, and `false` for types that do not. Such specializations shall be usable in constant expressions ([expr.const]) and have type `const bool`.

[ Hagenberg 2025-02-11; move to Ready ]

[ 2025-02-07; Reflector poll ]

Set priority to 1 after reflector poll.

Imported from cplusplus/sender-receiver #305 and cplusplus/sender-receiver #306.

We require an opt-in to satisfy the `sender` concept. Making your type awaitable with an empty environment is one way to opt in. If your awaitable requires an environment, you have two options:

• give your awaitable type a nested `sender_concept` typedef, or
• specialize `enable_sender` for your awaitable type.