constexpr swapSection: 22.2.2 [utility.swap] Status: Resolved Submitter: United States Opened: 2016-11-09 Last modified: 2020-09-06
Priority: 3
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Discussion:
Addresses US 108
swap is a critical function in the standard library, and
should be declared constexpr to support more
widespread support for constexpr in libraries. This
was proposed in P0202R1 which was reviewed
favourably at Oulu, but the widespread changes to
the <algorithm> header were too risky and unproven
for C++17. We should not lose constexpr support for
the much simpler (and more important) <utility>
functions because they were attached to a larger
paper. Similarly, the fundamental value wrappers, pair and tuple,
should have constexpr swap functions,
and the same should be considered for optional and
variant. It is not possible to mark swap for std::array
as constexpr without adopting the rest of the
P0202R1 though, or rewriting the specification
for array swap to not use swap_ranges.
Suggested resolution:
Adopt the changes to the<utility> header proposed in
P0202R1, i.e., only bullets C, D, and E.
In addition, mark the swap functions of pair and
tuple as constexpr, and consider doing the same for
optional and variant.
[Issues Telecon 16-Dec-2016]
Priority 3
[2017-11 Albuquerque Wednesday issue processing]
Status to Open; we don't want to do this yet; gated on Core issue 1581. See also 2897.
[2017-11 Albuquerque Thursday]
It looks like 1581 is going to be resolved this week, so we should revisit soon.
[2018-06]
Resolved by the adoption of P0879R0
Proposed resolution: