LWG4383 constant_wrapper's pseudo-mutators are underconstrained

Author: burblebee

source/meta.tex

@@ -778,62 +778,47 @@
     // pseudo-mutators
     template<@\exposconcept{constexpr-param}@ T>
       constexpr auto operator++(this T) noexcept
-        requires requires(T::value_type x) { ++x; }
-          { return constant_wrapper<[] { auto c = T::value; return ++c; }()>{}; }
+        -> constant_wrapper<++Y> { return {}; }
     template<@\exposconcept{constexpr-param}@ T>
       constexpr auto operator++(this T, int) noexcept
-        requires requires(T::value_type x) { x++; }
-          { return constant_wrapper<[] { auto c = T::value; return c++; }()>{}; }
-
+        -> constant_wrapper<Y++> { return {}; }
     template<@\exposconcept{constexpr-param}@ T>
       constexpr auto operator--(this T) noexcept
-        requires requires(T::value_type x) { --x; }
-          { return constant_wrapper<[] { auto c = T::value; return --c; }()>{}; }
+        -> constant_wrapper<--Y> { return {}; }
     template<@\exposconcept{constexpr-param}@ T>
       constexpr auto operator--(this T, int) noexcept
-        requires requires(T::value_type x) { x--; }
-          { return constant_wrapper<[] { auto c = T::value; return c--; }()>{}; }
+        -> constant_wrapper<Y--> { return {}; }
 
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator+=(this T, R) noexcept
-        requires requires(T::value_type x) { x += R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v += R::value; }()>{}; }
+      constexpr auto operator+=(T, R) noexcept
+        -> constant_wrapper<(T::value += R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator-=(this T, R) noexcept
-        requires requires(T::value_type x) { x -= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v -= R::value; }()>{}; }
+      constexpr auto operator-=(T, R) noexcept
+        -> constant_wrapper<(T::value -= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator*=(this T, R) noexcept
-        requires requires(T::value_type x) { x *= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v *= R::value; }()>{}; }
+      constexpr auto operator*=(T, R) noexcept
+        -> constant_wrapper<(T::value *= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator/=(this T, R) noexcept
-        requires requires(T::value_type x) { x /= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v /= R::value; }()>{}; }
+      constexpr auto operator/=(T, R) noexcept
+        -> constant_wrapper<(T::value /= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator%=(this T, R) noexcept
-        requires requires(T::value_type x) { x %= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v %= R::value; }()>{}; }
+      constexpr auto operator%=(T, R) noexcept
+        -> constant_wrapper<(T::value %= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator&=(this T, R) noexcept
-        requires requires(T::value_type x) { x &= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v &= R::value; }()>{}; }
+      constexpr auto operator&=(T, R) noexcept
+        -> constant_wrapper<(T::value &= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator|=(this T, R) noexcept
-        requires requires(T::value_type x) { x |= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v |= R::value; }()>{}; }
+      constexpr auto operator|=(T, R) noexcept
+        -> constant_wrapper<(T::value |= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator^=(this T, R) noexcept
-        requires requires(T::value_type x) { x ^= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v ^= R::value; }()>{}; }
+      constexpr auto operator^=(T, R) noexcept
+        -> constant_wrapper<(T::value ^= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator<<=(this T, R) noexcept
-        requires requires(T::value_type x) { x <<= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v <<= R::value; }()>{}; }
+      constexpr auto operator<<=(T, R) noexcept
+        -> constant_wrapper<(T::value <<= R::value)> { return {}; }
     template<@\exposconcept{constexpr-param}@ T, @\exposconcept{constexpr-param}@ R>
-      constexpr auto operator>>=(this T, R) noexcept
-        requires requires(T::value_type x) { x >>= R::value; }
-          { return constant_wrapper<[] { auto v = T::value; return v >>= R::value; }()>{}; }
+      constexpr auto operator>>=(T, R) noexcept
+        -> constant_wrapper<(T::value >>= R::value)> { return {}; }
   };
 
   template<@\exposid{cw-fixed-value}@ X, class>
@@ -844,8 +829,7 @@
 
     template<@\exposconcept{constexpr-param}@ R>
       constexpr auto operator=(R) const noexcept
-        requires requires(value_type x) { x = R::value; }
-          { return constant_wrapper<[] { auto v = value; return v = R::value; }()>{}; }
+        -> constant_wrapper<X = R::value> { return {}; }
 
     constexpr operator decltype(auto)() const noexcept { return value; }
   };