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P3383R3 mdspan.at() #7991

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72 changes: 70 additions & 2 deletions source/containers.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -21034,7 +21034,7 @@

\indexheader{mdspan}%
\begin{codeblock}
// all freestanding
// mostly freestanding
namespace std {
// \ref{mdspan.extents}, class template \tcode{extents}
template<class IndexType, size_t... Extents>
Expand Down Expand Up @@ -21068,7 +21068,7 @@
// \ref{mdspan.mdspan}, class template \tcode{mdspan}
template<class ElementType, class Extents, class LayoutPolicy = layout_right,
class AccessorPolicy = default_accessor<ElementType>>
class mdspan;
class mdspan; // partially freestanding

// \ref{mdspan.sub}, \tcode{submdspan} creation
template<class OffsetType, class LengthType, class StrideType>
Expand Down Expand Up @@ -24691,6 +24691,13 @@
template<class OtherIndexType>
constexpr reference operator[](const array<OtherIndexType, rank()>& indices) const;

template<class... OtherIndexTypes>
constexpr reference at(OtherIndexTypes... indices) const; // freestanding-deleted
template<class OtherIndexType>
constexpr reference at(span<OtherIndexType, rank()> indices) const; // freestanding-deleted
template<class OtherIndexType>
constexpr reference at(const array<OtherIndexType, rank()>& indices) const; // freestanding-deleted

constexpr size_type size() const noexcept;
constexpr bool empty() const noexcept;

Expand Down Expand Up @@ -25139,6 +25146,67 @@
\end{codeblock}
\end{itemdescr}

\indexlibrarymember{at}{mdspan}%
\begin{itemdecl}
template<class... OtherIndexTypes>
constexpr reference at(OtherIndexTypes... indices) const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\constraints
\begin{itemize}
\item
\tcode{(is_convertible_v<OtherIndexTypes, index_type> \&\& ...)} is \tcode{true},
\item
\tcode{(is_nothrow_constructible_v<index_type, OtherIndexTypes> \&\& ...)} is \tcode{true}, and
\item
\tcode{sizeof...(OtherIndexTypes) == rank()} is \tcode{true}.
\end{itemize}

\pnum
Let \tcode{I} be \tcode{extents_type::\exposid{index-cast}(std::move(indices))}.

\pnum
\returns
\tcode{(*this)[I...]}.

\pnum
\throws
\tcode{out_of_range} if \tcode{I} is not a multidimensional index in \tcode{extents()}.
\end{itemdescr}

\indexlibrarymember{at}{mdspan}%
\begin{itemdecl}
template<class OtherIndexType>
constexpr reference at(span<OtherIndexType, rank()> indices) const;
template<class OtherIndexType>
constexpr reference at(const array<OtherIndexType, rank()>& indices) const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\constraints
\begin{itemize}
\item
\tcode{is_convertible_v<const OtherIndexType\&, index_type>} is \tcode{true}, and
\item
\tcode{is_nothrow_constructible_v<index_type, const OtherIndexType\&>} is \tcode{true}.
\end{itemize}

\pnum
\effects
Let \tcode{P} be a parameter pack such that
\begin{codeblock}
is_same_v<make_index_sequence<rank()>, index_sequence<P...>>
\end{codeblock}
is \tcode{true}.
Equivalent to:
\begin{codeblock}
return at(extents_type::@\exposid{index-cast}@(as_const(indices[P]))...);
\end{codeblock}
\end{itemdescr}

\indexlibrarymember{size}{mdspan}%
\begin{itemdecl}
constexpr size_type size() const noexcept;
Expand Down
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