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LWG Poll 16: P1976R2 Fixed-size span construction from dynamic range #3772

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merged 2 commits into from
Mar 3, 2020
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LWG Poll 16: P1976R2 Fixed-size span construction from dynamic range #3772

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0f43312
P1976R2 Fixed-size span construction from dynamic range
jwakely Mar 3, 2020
8dc2366
[span.sub], [span.objectrep] Use direct-list-initialization in span
zygoloid Mar 3, 2020
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60 changes: 43 additions & 17 deletions source/containers.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -10669,20 +10669,20 @@
// \ref{span.cons}, constructors, copy, and assignment
constexpr span() noexcept;
template<class It>
constexpr span(It first, size_type count);
constexpr explicit(extent != dynamic_extent) span(It first, size_type count);
template<class It, class End>
constexpr span(It first, End last);
constexpr explicit(extent != dynamic_extent) span(It first, End last);
template<size_t N>
constexpr span(type_identity_t<element_type> (&arr)[N]) noexcept;
template<class T, size_t N>
constexpr span(array<T, N>& arr) noexcept;
template<class T, size_t N>
constexpr span(const array<T, N>& arr) noexcept;
template<class R>
constexpr span(R&& r);
constexpr explicit(extent != dynamic_extent) span(R&& r);
constexpr span(const span& other) noexcept = default;
template<class OtherElementType, size_t OtherExtent>
constexpr span(const span<OtherElementType, OtherExtent>& s) noexcept;
constexpr explicit(@\seebelow@) span(const span<OtherElementType, OtherExtent>& s) noexcept;

~span() noexcept = default;

Expand Down Expand Up @@ -10760,7 +10760,7 @@
\indexlibraryctor{span}%
\begin{itemdecl}
template<class It>
constexpr span(It first, size_type count);
constexpr explicit(extent != dynamic_extent) span(It first, size_type count);
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -10800,7 +10800,7 @@
\indexlibraryctor{span}%
\begin{itemdecl}
template<class It, class End>
constexpr span(It first, End last);
constexpr explicit(extent != dynamic_extent) span(It first, End last);
\end{itemdecl}

\begin{itemdescr}
Expand Down Expand Up @@ -10850,9 +10850,14 @@
\begin{itemdescr}
\pnum
\constraints
Let \tcode{U} be \tcode{remove_pointer_t<decltype(data(arr))>}.
\begin{itemize}
\item \tcode{extent == dynamic_extent || N == extent} is \tcode{true}, and
\item \tcode{remove_pointer_t<decltype(data(arr))>(*)[]} is convertible to \tcode{ElementType(*)[]}.
\item \tcode{is_convertible_v<U(*)[], element_type(*)[]>} is \tcode{true}.
\begin{note}
The intent is to allow only qualification conversions
of the array element type to \tcode{element_type}.
\end{note}
\end{itemize}

\pnum
Expand All @@ -10869,15 +10874,14 @@

\indexlibraryctor{span}%
\begin{itemdecl}
template<class R> constexpr span(R&& r);
template<class R> constexpr explicit(extent != dynamic_extent) span(R&& r);
\end{itemdecl}

\begin{itemdescr}
\pnum
\constraints
Let \tcode{U} be \tcode{remove_reference_t<ranges::range_reference_t<R>>}.
\begin{itemize}
\item \tcode{extent == dynamic_extent} is \tcode{true}.
\item \tcode{R} satisfies \tcode{ranges::\libconcept{contiguous_range}} and
\tcode{ranges::\libconcept{sized_range}}.
\item Either \tcode{R} satisfies \tcode{ranges::\libconcept{borrowed_range}} or
Expand All @@ -10889,13 +10893,15 @@
\tcode{is_convertible_v<U(*)[], element_type(*)[]>} is \tcode{true}.
\begin{note}
The intent is to allow only qualification conversions
of the iterator reference type to \tcode{element_type}.
of the range reference type to \tcode{element_type}.
\end{note}
\end{itemize}

\pnum
\expects
\begin{itemize}
\item If \tcode{extent} is not equal to \tcode{dynamic_extent},
then \tcode{ranges::size(r)} is equal to \tcode{extent}.
\item \tcode{R} models \tcode{ranges::\libconcept{contiguous_range}} and
\tcode{ranges::\libconcept{sized_range}}.
\item If \tcode{is_const_v<element_type>} is \tcode{false},
Expand Down Expand Up @@ -10926,17 +10932,26 @@
\indexlibraryctor{span}%
\begin{itemdecl}
template<class OtherElementType, size_t OtherExtent>
constexpr span(const span<OtherElementType, OtherExtent>& s) noexcept;
constexpr explicit(@\seebelow@) span(const span<OtherElementType, OtherExtent>& s) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\constraints
\begin{itemize}
\item \tcode{Extent == dynamic_extent || Extent == OtherExtent} is \tcode{true}, and
\item \tcode{OtherElementType(*)[]} is convertible to \tcode{ElementType(*)[]}.
\item \tcode{extent == dynamic_extent} \tcode{||} \tcode{OtherExtent == dynamic_extent} \tcode{||} \tcode{extent == OtherExtent} is \tcode{true}, and
\item \tcode{is_convertible_v<OtherElementType(*)[], element_type(*)[]>} is \tcode{true}.
\begin{note}
The intent is to allow only qualification conversions
of the \tcode{OtherElementType} to \tcode{element_type}.
\end{note}
\end{itemize}

\pnum
\expects
If \tcode{extent} is not equal to \tcode{dynamic_extent},
then \tcode{s.size()} is equal to \tcode{extent}.

\pnum
\effects
Constructs a \tcode{span} that is a view over the range
Expand All @@ -10945,6 +10960,13 @@
\pnum
\ensures
\tcode{size() == s.size() \&\& data() == s.data()}.

\pnum
\remarks
The expression inside \tcode{explicit} is equivalent to:
\begin{codeblock}
extent != dynamic_extent && OtherExtent == dynamic_extent
\end{codeblock}
\end{itemdescr}

\indexlibrarymember{operator=}{span}%
Expand Down Expand Up @@ -11002,7 +11024,8 @@

\pnum
\effects
Equivalent to: \tcode{return \{data(), Count\};}
Equivalent to: \tcode{return R\{data(), Count\};}
where \tcode{R} is the return type.
\end{itemdescr}

\indexlibrarymember{span}{last}%
Expand All @@ -11021,7 +11044,8 @@

\pnum
\effects
Equivalent to: \tcode{return \{data() + (size() - Count), Count\};}
Equivalent to: \tcode{return R\{data() + (size() - Count), Count\};}
where \tcode{R} is the return type.
\end{itemdescr}

\indexlibrarymember{span}{subspan}%
Expand Down Expand Up @@ -11287,7 +11311,8 @@
\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return \{reinterpret_cast<const byte*>(s.data()), s.size_bytes()\};}
Equivalent to: \tcode{return R\{reinterpret_cast<const byte*>(s.data()), s.size_bytes()\};}
where \tcode{R} is the return type.
\end{itemdescr}

\indexlibraryglobal{as_writable_bytes}%
Expand All @@ -11304,7 +11329,8 @@

\pnum
\effects
Equivalent to: \tcode{return \{reinterpret_cast<byte*>(s.data()), s.size_bytes()\};}
Equivalent to: \tcode{return R\{reinterpret_cast<byte*>(s.data()), s.size_bytes()\};}
where \tcode{R} is the return type.
\end{itemdescr}

\rSec3[span.tuple]{Tuple interface}
Expand Down
2 changes: 1 addition & 1 deletion source/support.tex
View file
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Original file line number Diff line number Diff line change
Expand Up @@ -670,7 +670,7 @@
#define @\defnlibxname{cpp_lib_shift}@ 201806L // also in \libheader{algorithm}
#define @\defnlibxname{cpp_lib_smart_ptr_default_init}@ 201811L // also in \libheader{memory}
#define @\defnlibxname{cpp_lib_source_location}@ 201907L // also in \libheader{source_location}
#define @\defnlibxname{cpp_lib_span}@ 201902L // also in \libheader{span}
#define @\defnlibxname{cpp_lib_span}@ 202002L // also in \libheader{span}
#define @\defnlibxname{cpp_lib_ssize}@ 201902L // also in \libheader{iterator}
#define @\defnlibxname{cpp_lib_starts_ends_with}@ 201711L // also in \libheader{string}, \libheader{string_view}
#define @\defnlibxname{cpp_lib_string_udls}@ 201304L // also in \libheader{string}
Expand Down