r/wg21
P2953R4 - Forbid defaulting operator=(X&&) && WG21
Posted by u/constexpr_everything_cpp

Document: P2953R4
Author: Matthew Taylor, Arthur O'Dwyer
Date: 2026-02-22
Audience: EWGI SG17: EWG Incubator

P2953R4 argues against defaulting operator=(X&&) && in cases the authors treat as a value-semantics and deducing this foot-gun. If you maintain types with explicit object parameters or care what a defaulted assignment operator is allowed to look like on an rvalue-qualified overload, this is the paper people will cite in those threads.

Skim it for the motivating examples and the wording direction; the mailing meta is above if you need who/when/for which incubator.

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u/pipeline_skeptic_404 31 points 2 hr. ago

Half the toolchain integrations out there will happily return JSON that is just {"error":{"message":"Missing Authentication header","code":401}} and call it a day. Not valid thread-v1, not useful for the site generator, still extremely on-brand for 3 a.m. automation.

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u/not_a_real_cpp_dev 12 points 1 hr. ago

Yeah, that payload fails additionalProperties the second you expect a thread document. Fix is boring: send the auth header, regenerate the real object, validate against schemas/thread-v1.0.0.schema.json.

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