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4208. Wording needs to ensure that inconnect(sndr, rcvr) that rcvr expression is only evaluated once
Section: 33.9.10 [exec.connect] Status: WP Submitter: Eric Niebler Opened: 2025-02-07 Last modified: 2025-06-23
Priority: Not Prioritized
View all issues with WP status.
Discussion:
Imported from cplusplus/sender-receiver #325.
The current wording of connect(sndr, rcvr) defines the new_sndr expression as transform_sender(decltype(get-domain-late(sndr, get_env(rcvr))){}, sndr, get_env(rcvr)).
connect(sndr, rcvr) as expression equivalent to new_sndr.connect(rcvr). As currently worded, this requires evaluating the rcvr expression twice. Note that the first usage in the new_sndr expression is unevaluated, but the second usage in get_env(rcvr) is evaluated. I think we need to add an extra sentence at the end of this section saying "Where the expression rcvr is only evaluated once." or similar.
[Hagenberg 2025-02-11; move to Ready]
[Sofia 2025-06-21; Status changed: Voting → WP.]
Proposed resolution:
This wording is relative to N5001.
Modify 33.9.10 [exec.connect] as indicated:
-6- The expression
connect(sndr, rcvr)is expression-equivalent to:
(6.1) —
Mandates: The type of the expression above satisfiesnew_sndr.connect(rcvr)if that expression is well-formed.operation_state.(6.2) — Otherwise,
connect-awaitable(new_sndr, rcvr).except that
Mandates:rcvris evaluated only once.sender<Sndr> && receiver<Rcvr>istrue.
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