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std::swap should not be supportedSection: 16.4.5.2.1 [namespace.std] Status: New Submitter: Jiang An Opened: 2024-01-25 Last modified: 2024-03-15
Priority: 4
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Discussion:
std::swap overloads are separately declared in many standard library headers. It is likely expected
that when a program includes correct headers for standard library types to be swapped, a std::swap call,
with template argument deduced from arguments, selects the correct overload.
std::swap call, there would be possibly
undesired overloads for which templates arguments are fully obtained, and thus undesired instantiation and
ill-formed may be triggered.
Perhaps we should explicitly state that explicitly specifying templates for std::swap is unsupported
(having unspecified effects and possibly ill-formed), like taking address of non-address functions
(16.4.5.2.1 [namespace.std]/6) and explicitly specifying template arguments for most standard algorithms
(26.2 [algorithms.requirements]/15), to avoid possible reading that there are some guarantees, derived
from signatures of overloads, for doing so.
[2024-03-15; Reflector poll]
Set priority to 4 after reflector poll.
NAD - if a user does this and it breaks, so be it.
NAD as an issue creating a new kind of library policy for the first time. Needs a paper.
Not unique to std::swap. We should forbid this throughout
the standard library.
Closely related to LWG 2146(i).
Proposed resolution: