P2613R1 Add the missing empty to mdspan

Author: jensmaurer

source/containers.tex

@@ -16997,6 +16997,7 @@
       constexpr reference operator[](const array<OtherIndexType, rank()>& indices) const;
 
     constexpr size_type size() const noexcept;
+    [[nodiscard]] constexpr bool empty() const noexcept;
 
     friend constexpr void swap(mdspan& x, mdspan& y) noexcept;
 
@@ -17460,6 +17461,19 @@
 \tcode{extents().\exposid{fwd-prod-of-extents}(rank())}.
 \end{itemdescr}
 
+\indexlibrarymember{empty}{mdspan}%
+\begin{itemdecl}
+[[nodiscard]] constexpr bool empty() const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{true}
+if the size of the multidimensional index space \tcode{extents()} is 0,
+otherwise \tcode{false}.
+\end{itemdescr}
+
 \indexlibrarymember{swap}{mdspan}%
 \begin{itemdecl}
 friend constexpr void swap(mdspan& x, mdspan& y) noexcept;