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split_view::outer_iterator
converting constructor is misconstrainedSection: 26.7.16.3 [range.lazy.split.outer] Status: NAD Submitter: Casey Carter Opened: 2019-01-05 Last modified: 2023-02-07
Priority: Not Prioritized
View all other issues in [range.lazy.split.outer].
View all issues with NAD status.
Discussion:
The constraints on split_view::outer_iterator
's converting constructor:
are problematic. Sinceconstexpr outer_iterator(outer_iterator<!Const> i) requires Const && ConvertibleTo<iterator_t<V>, iterator_t<const V>>;
const V
doesn't depend on a template parameter
of outer_iterator
, compilers want to expand
iterator_t<const V>
when outer_iterator
is instantiated
- regardless of the value of Const
- which can result in a hard error
when iterator_t<const V>
is ill-formed. The constraint should
instead use iterator_t<Base>
, as do the similar converting
constructors for the other range adaptor iterator and sentinel types.
[2019-01-20 Reflector prioritization]
Set status to NAD
Proposed resolution:
This wording is relative to N4791.
Change [range.split.outer] as follows:
namespace std::ranges { template<class V, class Pattern> template<bool Const> struct split_view<V, Pattern>::outer_iterator { […] constexpr outer_iterator(outer_iterator<!Const> i) requires Const && ConvertibleTo<iterator_t<V>, iterator_t<const VBase>>; […] }; }[…]
constexpr outer_iterator(outer_iterator<!Const> i) requires Const && ConvertibleTo<iterator_t<V>, iterator_t<const VBase>>;-4- Effects: Initializes
parent_
withi.parent_
andcurrent_
withstd::move(i.current_)
.[…]