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reverse_iterator::operator->
is underconstrained for non-pointer iteratorsSection: 25.5.1.6 [reverse.iter.elem] Status: NAD Submitter: Hewill Kang Opened: 2022-06-27 Last modified: 2022-11-30
Priority: Not Prioritized
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Discussion:
For non-pointer types, reverse_iterator::operator->
only requires the expression
i.operator->()
to be well-formed.
pointer
,
this will cause a hard error in the function body when the return type of i.operator->()
cannot be converted to pointer
.
We should add a return type constraint for this.
[2022-08-23; Reflector poll: NAD]
pointer
is iterator_traits<Iterator>::pointer
,
which is required to name decltype(i.operator->())
(25.3.2.3 [iterator.traits]/1)
so the postulated problem simply does not arise in valid code.
[2022-11-30 LWG telecon. Status changed: Tentatively NAD → NAD.]
Proposed resolution:
This wording is relative to N4910.
Modify 25.5.1.6 [reverse.iter.elem] as indicated:
constexpr pointer operator->() const requires (is_pointer_v<Iterator> || requires(const Iterator i) { { i.operator->() } -> convertible_to<pointer>; });-2- Effects:
(2.1) — If
Iterator
is a pointer type, equivalent to:return prev(current);
(2.2) — Otherwise, equivalent to:
return prev(current).operator->();