Fix to 2013-09 LWG Motion 7:

[comparisons] Fix incorrect application of N3789 to the working paper:
  - Add 'constexpr' to
      std::equal_to<>::operator()
      std::not_equal_to<>::operator()
      std::greater<>::operator()
      std::less<>::operator()
      std::greater_equal<>::operator()
      std::less_equal<>::operator()
  - Reorder 'bool constexpr' to 'constexpr bool' in
      std::logical_or<T>::operator()
      std::logical_and<T>::operator()
      std::logical_not<T>::operator()

Also fixes 14882:2014 DIS JP 08, fixes 14882:2014 DIS JP 09, fixes #291.

Author: zygoloid

source/utilities.tex

@@ -7811,7 +7811,7 @@
 \indexlibrary{\idxcode{equal_to<>}}%
 \begin{itemdecl}
 template <> struct equal_to<void> {
-  template <class T, class U> auto operator()(T&& t, U&& u) const
+  template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
     -> decltype(std::forward<T>(t) == std::forward<U>(u));
 
   typedef @\unspec@ is_transparent;
@@ -7826,7 +7826,7 @@
 \indexlibrary{\idxcode{not_equal_to<>}}%
 \begin{itemdecl}
 template <> struct not_equal_to<void> {
-  template <class T, class U> auto operator()(T&& t, U&& u) const
+  template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
     -> decltype(std::forward<T>(t) != std::forward<U>(u));
 
   typedef @\unspec@ is_transparent;
@@ -7841,7 +7841,7 @@
 \indexlibrary{\idxcode{greater<>}}%
 \begin{itemdecl}
 template <> struct greater<void> {
-  template <class T, class U> auto operator()(T&& t, U&& u) const
+  template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
     -> decltype(std::forward<T>(t) > std::forward<U>(u));
 
   typedef @\unspec@ is_transparent;
@@ -7856,7 +7856,7 @@
 \indexlibrary{\idxcode{less<>}}%
 \begin{itemdecl}
 template <> struct less<void> {
-  template <class T, class U> auto operator()(T&& t, U&& u) const
+  template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
     -> decltype(std::forward<T>(t) < std::forward<U>(u));
 
   typedef @\unspec@ is_transparent;
@@ -7871,7 +7871,7 @@
 \indexlibrary{\idxcode{greater_equal<>}}%
 \begin{itemdecl}
 template <> struct greater_equal<void> {
-  template <class T, class U> auto operator()(T&& t, U&& u) const
+  template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
     -> decltype(std::forward<T>(t) >= std::forward<U>(u));
 
   typedef @\unspec@ is_transparent;
@@ -7886,7 +7886,7 @@
 \indexlibrary{\idxcode{less_equal<>}}%
 \begin{itemdecl}
 template <> struct less_equal<void> {
-  template <class T, class U> auto operator()(T&& t, U&& u) const
+  template <class T, class U> constexpr auto operator()(T&& t, U&& u) const
     -> decltype(std::forward<T>(t) <= std::forward<U>(u));
 
   typedef @\unspec@ is_transparent;
@@ -7913,7 +7913,7 @@
 \indexlibrary{\idxcode{logical_and}}%
 \begin{itemdecl}
 template <class T = void> struct logical_and {
-  bool constexpr operator()(const T& x, const T& y) const;
+  constexpr bool operator()(const T& x, const T& y) const;
   typedef T first_argument_type;
   typedef T second_argument_type;
   typedef bool result_type;
@@ -7928,7 +7928,7 @@
 \indexlibrary{\idxcode{logical_or}}%
 \begin{itemdecl}
 template <class T = void> struct logical_or {
-  bool constexpr operator()(const T& x, const T& y) const;
+  constexpr bool operator()(const T& x, const T& y) const;
   typedef T first_argument_type;
   typedef T second_argument_type;
   typedef bool result_type;
@@ -7943,7 +7943,7 @@
 \indexlibrary{\idxcode{logical_not}}%
 \begin{itemdecl}
 template <class T = void> struct logical_not {
-  bool constexpr operator()(const T& x) const;
+  constexpr bool operator()(const T& x) const;
   typedef T argument_type;
   typedef bool result_type;
 };