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proxy
and postfix-proxy
for common_iterator
should be fully constexpr
Section: 25.5.5.4 [common.iter.access], 25.5.5.5 [common.iter.nav] Status: C++23 Submitter: Hewill Kang Opened: 2021-09-18 Last modified: 2023-11-22
Priority: Not Prioritized
View all other issues in [common.iter.access].
View all issues with C++23 status.
Discussion:
LWG 3574(i) added constexpr
to all member functions and friends of common_iterator
to make it
fully constexpr
, but accidentally omitted the exposition-only classes proxy
and
postfix-proxy
defined for some member functions. We should make these two classes fully constexpr
, too.
[2021-09-24; Reflector poll]
Set status to Tentatively Ready after seven votes in favour during reflector poll.
[2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting → WP.]
Proposed resolution:
This wording is relative to N4892.
Modify 25.5.5.4 [common.iter.access] as indicated:
decltype(auto) operator->() const requires see below;-3- […]
-4- […] -5- Effects:
(5.1) — […]
(5.2) — […]
(5.3) — Otherwise, equivalent to:
return proxy(*get<I>(v_));
whereproxy
is the exposition-only class:class proxy { iter_value_t<I> keep_; constexpr proxy(iter_reference_t<I>&& x) : keep_(std::move(x)) {} public: constexpr const iter_value_t<I>* operator->() const noexcept { return addressof(keep_); } };
Modify 25.5.5.5 [common.iter.nav] as indicated:
decltype(auto) operator++(int);-4- […]
-5- Effects: If I models forward_iterator, equivalent to: […] Otherwise, if […] […] Otherwise, equivalent to:postfix-proxy p(**this); ++*this; return p;where
postfix-proxy
is the exposition-only class:class postfix-proxy { iter_value_t<I> keep_; constexpr postfix-proxy(iter_reference_t<I>&& x) : keep_(std::forward<iter_reference_t<I>>(x)) {} public: constexpr const iter_value_t<I>& operator*() const noexcept { return keep_; } };