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LWG Motion 37: P4159R0 Make sender_in and receiver_of exposition-only #8958

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Merged
tkoeppe merged 2 commits into from
Apr 20, 2026
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LWG Motion 37: P4159R0 Make sender_in and receiver_of exposition-only #8958

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9a416a6
P4159R0 Make `sender_in` and `receiver_of` exposition-only
tkoeppe Apr 20, 2026
ccea75a
[exec.snd.concepts, exec.recv.concepts] Insert "exposition-only"
tkoeppe Apr 20, 2026
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32 changes: 16 additions & 16 deletions source/exec.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -510,7 +510,7 @@
concept @\libconcept{receiver}@ = @\seebelow@;

template<class Rcvr, class Completions>
concept @\libconcept{receiver_of}@ = @\seebelow@;
concept @\exposconceptnc{receiver-of}@ = @\seebelownc@; // \expos

template<class Rcvr, class ChildOp>
concept @\libconcept{inlinable_receiver}@ = @\seebelow@;
Expand Down Expand Up @@ -548,7 +548,7 @@
concept @\libconcept{dependent_sender}@ = @\seebelow@;

template<class Sndr, class Rcvr>
concept @\libconcept{sender_to}@ = @\seebelow@;
concept @\exposconceptnc{sender-to}@ = @\seebelownc@; // \expos

template<class... Ts>
struct @\exposidnc{type-list}@; // \expos
Expand Down Expand Up @@ -578,7 +578,7 @@
using @\exposidnc{single-sender-value-type}@ = @\seebelownc@; // \expos

template<class Sndr, class... Env>
concept @\exposconcept{single-sender}@ = @\seebelow@; // \expos
concept @\exposconceptnc{single-sender}@ = @\seebelownc@; // \expos

@RobertLeahy RobertLeahy Apr 20, 2026

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This is a drive by?

@tkoeppe tkoeppe Apr 20, 2026

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Just whitespace, yes. The comment wasn't aligned properly.


template<@\libconcept{sender}@ Sndr>
using tag_of_t = @\seebelow@;
Expand Down Expand Up @@ -1012,7 +1012,7 @@

\pnum
Given subexpressions \tcode{sndr} and \tcode{rcvr}
such that \tcode{sender_to<decltype((sndr)), decltype((rcvr))>} is \tcode{true}
such that \tcode{\exposid{sender-to}<decltype((sndr)), decltype((rcvr))>} is \tcode{true}

@eisenwave eisenwave Apr 20, 2026

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Suggested change
such that \tcode{\exposid{sender-to}<decltype((sndr)), decltype((rcvr))>} is \tcode{true}
such that \tcode{\exposconcept{sender-to}<decltype((sndr)), decltype((rcvr))>} is \tcode{true}

and the expression \tcode{get_start_scheduler(get_env(rcvr))} is well-formed,
an operation state that is the result of calling \tcode{connect(sndr, rcvr)}
shall, if it is started, be started on an execution agent
Expand Down Expand Up @@ -1357,7 +1357,7 @@
A receiver represents the continuation of an asynchronous operation.
The \libconcept{receiver} concept defines
the requirements for a receiver type\iref{exec.async.ops}.
The \libconcept{receiver_of} concept defines
The exposition-only concept \exposconcept{receiver-of} defines
the requirements for a receiver type that is usable as
the first argument of a set of completion operations
corresponding to a set of completion signatures.
Expand Down Expand Up @@ -1391,7 +1391,7 @@
};

template<class Rcvr, class Completions>
concept @\deflibconcept{receiver_of}@ =
concept @\defexposconcept{receiver-of}@ =
@\libconcept{receiver}@<Rcvr> && @\exposconcept{has-completions}@<Rcvr, Completions>;
}
\end{codeblock}
Expand Down Expand Up @@ -1619,7 +1619,7 @@
let \tcode{Sndr} be \tcode{decltype((sndr))}.
Let \tcode{rcvr} be a receiver of type \tcode{Rcvr}
with associated environment \tcode{env} of type \tcode{Env}
such that \tcode{\libconcept{sender_to}<Sndr, Rcvr>} is \tcode{true}.
such that \tcode{\exposconcept{sender-to}<Sndr, Rcvr>} is \tcode{true}.
For the default implementation of the algorithm that produced \tcode{sndr},
connecting \tcode{sndr} to \tcode{rcvr} and
starting the resulting operation state\iref{exec.async.ops}
Expand Down Expand Up @@ -2477,7 +2477,7 @@
The \libconcept{sender_in} concept defines
the requirements for a sender type
that can create asynchronous operations given an associated environment type.
The \libconcept{sender_to} concept defines
The exposition-only concept \exposconcept{sender-to} defines
the requirements for a sender type
that can connect with a specific receiver type.
The \tcode{get_env} customization point object is used to access
Expand Down Expand Up @@ -2532,9 +2532,9 @@
@\libconcept{sender}@<Sndr> && bool_constant<@\exposid{is-dependent-sender-helper}@<Sndr>()>::value;

template<class Sndr, class Rcvr>
concept @\deflibconcept{sender_to}@ =
concept @\defexposconcept{sender-to}@ =
@\libconcept{sender_in}@<Sndr, env_of_t<Rcvr>> &&
@\libconcept{receiver_of}@<Rcvr, completion_signatures_of_t<Sndr, env_of_t<Rcvr>>> &&
@\exposconcept{receiver-of}@<Rcvr, completion_signatures_of_t<Sndr, env_of_t<Rcvr>>> &&
requires (Sndr&& sndr, Rcvr&& rcvr) {
connect(std::forward<Sndr>(sndr), std::forward<Rcvr>(rcvr));
};
Expand Down Expand Up @@ -3199,7 +3199,7 @@
return awaiter{fn};
}

@\exposid{operation-state-task}@ @\exposid{connect-awaitable}@(DS sndr, DR rcvr) requires @\libconcept{receiver_of}@<DR, Sigs> {
@\exposid{operation-state-task}@ @\exposid{connect-awaitable}@(DS sndr, DR rcvr) requires @\exposconcept{receiver-of}@<DR, Sigs> {
exception_ptr ep;
try {
if constexpr (@\libconcept{same_as}@<V, void>) {
Expand Down Expand Up @@ -3251,7 +3251,7 @@
\item
\tcode{\libconcept{sender_in}<Sndr, env_of_t<Rcvr>>}
\item
\tcode{\libconcept{receiver_of}<Rcvr, completion_signatures_of_t<Sndr, env_of_t<Rcvr>>>}
\tcode{\exposconcept{receiver-of}<Rcvr, completion_signatures_of_t<Sndr, env_of_t<Rcvr>>>}
\end{itemize}

\rSec2[exec.factories]{Sender factories}
Expand Down Expand Up @@ -6153,7 +6153,7 @@

\pnum
For a subexpression \tcode{sndr}, let \tcode{Sndr} be \tcode{decltype((sndr))}.
If \tcode{\libconcept{sender_to}<Sndr, \exposid{sync-wait-receiver}<\linebreak Sndr>>}
If \tcode{\exposconcept{sender-to}<Sndr, \exposid{sync-wait-receiver}<\linebreak Sndr>>}
is \tcode{false},
the expression \tcode{sync_wait.apply_sender(sndr)} is ill-formed;
otherwise, it is equivalent to:
Expand Down Expand Up @@ -6831,7 +6831,7 @@
\pnum
Let \exposid{sndr} be an expression of type \exposid{run-loop-sender},
let \exposid{rcvr} be an expression
such that \tcode{\libconcept{receiver_of}<decltype((\exposid{rcvr})), CS>} is \tcode{true}
such that \tcode{\exposconcept{receiver-of}<decl\-type((\exposid{rcvr})), CS>} is \tcode{true}
where \tcode{CS} is the \tcode{completion_signatures} specialization above.
Let \tcode{C} be either \tcode{set_value_t} or \tcode{set_stopped_t}.
Then:
Expand Down Expand Up @@ -7027,7 +7027,7 @@
template<class Sndr, class Promise>
concept @\defexposconcept{awaitable-sender}@ =
@\exposconcept{single-sender}@<Sndr, env_of_t<Promise>> &&
@\libconcept{sender_to}@<Sndr,
@\exposconcept{sender-to}@<Sndr,
typename @\exposid{sender-awaitable}@<Sndr, Promise>::@\exposid{awaitable-receiver}@> && // \seebelow
requires (Promise& p) {
{ p.unhandled_stopped() } -> @\libconcept{convertible_to}@<coroutine_handle<>>;
Expand Down Expand Up @@ -7422,7 +7422,7 @@
\pnum
Let \tcode{sndr} be an expression of type \exposid{inline-sender},
let \tcode{rcvr} be an expression such that
\tcode{\libconcept{receiver_of}<decltype((rcvr)), CS>} is \tcode{true}
\tcode{\exposconcept{receiver-of}<decl\-type((rcvr)), CS>} is \tcode{true}
where \tcode{CS} is \tcode{completion_signatures<set_value_t()>},
then the expression \tcode{connect(sndr, rcvr)} has
type \tcode{\exposid{inline-state}<remove_cvref_t<decltype((rcvr))>>}
Expand Down
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