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Section: 23.4.3 [basic.string], 26.7.14.2 [range.join.view] Status: New Submitter: Johel Ernesto Guerrero Peña Opened: 2020-06-11 Last modified: 2020-07-17
Priority: 3
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Discussion:
The library inconsistently marks deduction guides as explicit
. join_view
and basic_string
account for the only two occurrences of unconditionally explicit deduction guides. All other deduction
guides have no explicit
-specifier. Following is a list of unconditionally explicit constructors
with their deduction guides.
template<class Y> explicit shared_ptr(const weak_ptr<Y>& r); template<class T> shared_ptr(weak_ptr<T>) -> shared_ptr<T>; template<class T> constexpr explicit basic_string(const T& t, const Allocator& a = Allocator()); template<class charT, class traits, class Allocator = allocator<charT>> explicit basic_string(basic_string_view<charT, traits>, const Allocator& = Allocator()) -> basic_string<charT, traits, Allocator>; explicit queue(const Container&); explicit queue(Container&&); template<class Container> queue(Container) -> queue<typename Container::value_type, Container>; explicit stack(const Container&); explicit stack(Container&&); template<class Container> stack(Container) -> stack<typename Container::value_type, Container>; constexpr explicit join_view(V base); template<class R> explicit join_view(R&&) -> join_view<views::all_t<R>>; constexpr explicit common_view(V r); template<class R> common_view(R&&) -> common_view<views::all_t<R>>; constexpr explicit reverse_view(V r); template<class R> reverse_view(R&&) -> reverse_view<views::all_t<R>>; explicit zoned_time(TimeZonePtr z); explicit zoned_time(string_view name); template<class TimeZonePtrOrName> zoned_time(TimeZonePtrOrName&&) -> zoned_time<seconds, time-zone-representation<TimeZonePtrOrName>>; template<class C> explicit stop_callback(const stop_token& st, C&& cb) noexcept(is_nothrow_constructible_v<Callback, C>); template<class C> explicit stop_callback(stop_token&& st, C&& cb) noexcept(is_nothrow_constructible_v<Callback, C>); template<class Callback> stop_callback(stop_token, Callback) -> stop_callback<Callback>;
[2020-07-17; Priority set to 3 in telecon]
Proposed resolution:
This wording is relative to N4861.
Modify 23.4.3 [basic.string], class template basic_string
synopsis, as indicated:
[…] template<class charT, class traits, class Allocator = allocator<charT>>explicitbasic_string(basic_string_view<charT, traits>, const Allocator& = Allocator()) -> basic_string<charT, traits, Allocator>; […]
Modify 23.4.3.3 [string.cons] as indicated:
[…] template<class charT, class traits, class Allocator = allocator<charT>>explicitbasic_string(basic_string_view<charT, traits>, const Allocator& = Allocator()) -> basic_string<charT, traits, Allocator>; […]-22- Constraints:
Allocator
is a type that qualifies as an allocator (24.2.2 [container.requirements.general]).
Modify 26.7.14.2 [range.join.view], class template join_view
synopsis, as indicated:
[…] template<class R>explicitjoin_view(R&&) -> join_view<views::all_t<R>>; […]