P0548R1 common_type and duration

Author: zygoloid

source/utilities.tex

@@ -16776,7 +16776,8 @@
 \item If \tcode{sizeof...(T)} is one, let \tcode{T0} denote the sole type
 constituting the pack \tcode{T}.
 The member \grammarterm{typedef-name} \tcode{type} shall denote the same
-type as \tcode{decay_t<T0>}.
+type, if any, as \tcode{common_type_t<T0, T0>};
+otherwise there shall be no member \tcode{type}.
 
 \item If \tcode{sizeof...(T)} is two,
 let the first and second types constituting \tcode{T} be denoted
@@ -16798,10 +16799,6 @@
 In either case, the member \grammarterm{typedef-name} \tcode{type} shall denote
 the same type, if any, as \tcode{C}.
 Otherwise, there shall be no member \tcode{type}.
-\begin{note}
-When \tcode{is_same_v<T1, T2>} is \tcode{true},
-the effect is equivalent to that of \tcode{common_type<T1>}.
-\end{note}
 
 \item If \tcode{sizeof...(T)} is greater than two,
 let \tcode{T1}, \tcode{T2}, and \tcode{R}, respectively,
@@ -16816,7 +16813,7 @@
 Note B: Notwithstanding the provisions of \ref{meta.type.synop}, and
 pursuant to \ref{namespace.std},
 a program may specialize \tcode{common_type<T1, T2>}
-for distinct types \tcode{T1} and \tcode{T2} such that
+for types \tcode{T1} and \tcode{T2} such that
 \tcode{is_same_v<T1, decay_t<T1>>} and
 \tcode{is_same_v<T2, decay_t<T2>>} are each \tcode{true}.
 \begin{note}
@@ -17629,7 +17626,7 @@
 class duration {
 public:
   using rep    = Rep;
-  using period = Period;
+  using period = typename Period::type;
 private:
   rep rep_;  // \expos
 public:
@@ -17647,8 +17644,8 @@
   constexpr rep count() const;
 
   // \ref{time.duration.arithmetic}, arithmetic
-  constexpr duration  operator+() const;
-  constexpr duration  operator-() const;
+  constexpr common_type_t<duration> operator+() const;
+  constexpr common_type_t<duration> operator-() const;
   constexpr duration& operator++();
   constexpr duration  operator++(int);
   constexpr duration& operator--();
@@ -17774,22 +17771,22 @@
 
 \indexlibrarymember{operator+}{duration}%
 \begin{itemdecl}
-constexpr duration operator+() const;
+constexpr common_type_t<duration> operator+() const;
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
-\returns \tcode{*this}.
+\returns \tcode{common_type_t<duration>(*this)}.
 \end{itemdescr}
 
 \indexlibrarymember{operator-}{duration}%
 \begin{itemdecl}
-constexpr duration operator-() const;
+constexpr common_type_t<duration> operator-() const;
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
-\returns \tcode{duration(-rep_)}.
+\returns \tcode{common_type_t<duration>(-rep_)}.
 \end{itemdescr}
 
 \indexlibrarymember{operator++}{duration}%