P1682R2 std::to_underlying for enumerations

Author: jwakely

source/support.tex

@@ -684,6 +684,7 @@
 #define @\defnlibxname{cpp_lib_to_address}@                        201711L // also in \libheader{memory}
 #define @\defnlibxname{cpp_lib_to_array}@                          201907L // also in \libheader{array}
 #define @\defnlibxname{cpp_lib_to_chars}@                          201611L // also in \libheader{charconv}
+#define @\defnlibxname{cpp_lib_to_underlying}@                     202102L // also in \libheader{utility}
 #define @\defnlibxname{cpp_lib_transformation_trait_aliases}@      201304L // also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_transparent_operators}@             201510L // also in \libheader{memory}, \libheader{functional}
 #define @\defnlibxname{cpp_lib_tuple_element_t}@                   201402L // also in \libheader{tuple}

source/utilities.tex

@@ -95,6 +95,10 @@
   template<class R, class T>
     constexpr bool in_range(T t) noexcept;
 
+  // \ref{utility.underlying}, to_underlying
+  template<class T>
+    constexpr underlying_type_t<T> to_underlying(T value) noexcept;
+
   // \ref{intseq}, compile-time integer sequences%
 \indexlibraryglobal{index_sequence}%
 \indexlibraryglobal{make_index_sequence}%
@@ -568,6 +572,20 @@
 \tcode{bool}.
 \end{note}
 
+\rSec2[utility.underlying]{Function template \tcode{to_underlying}}
+
+\begin{itemdecl}
+template<class T>
+  constexpr underlying_type_t<T> to_underlying(T value) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{static_cast<underlying_type_t<T>>(value)}.
+\end{itemdescr}
+
+
 \rSec1[intseq]{Compile-time integer sequences}
 
 \rSec2[intseq.general]{In general}