Merge remote-tracking branch 'origin/kitsune/c++20-galore' into dev

1 files changed, 18 insertions, 18 deletions

diff --git a/lib/function_traits.h b/lib/function_traits.h
index 83b8e425..143ed162 100644
--- a/lib/function_traits.h
+++ b/lib/function_traits.h
@@ -8,7 +8,7 @@
 namespace Quotient {
 
 namespace _impl {
-    template <typename AlwaysVoid, typename>
+    template <typename>
     struct fn_traits {};
 }
 
@@ -21,73 +21,73 @@ namespace _impl {
  */
 template <typename T>
 struct function_traits
-    : public _impl::fn_traits<void, std::remove_reference_t<T>> {};
+    : public _impl::fn_traits<std::remove_reference_t<T>> {};
 
 // Specialisation for a function
 template <typename ReturnT, typename... ArgTs>
 struct function_traits<ReturnT(ArgTs...)> {
     using return_type = ReturnT;
     using arg_types = std::tuple<ArgTs...>;
-    // See also the comment for wrap_in_function() in qt_connection_util.h
-    using function_type = std::function<ReturnT(ArgTs...)>;
 };
 
 namespace _impl {
-    template <typename AlwaysVoid, typename>
+    template <typename>
     struct fn_object_traits;
 
     // Specialisation for a lambda function
     template <typename ReturnT, typename ClassT, typename... ArgTs>
-    struct fn_object_traits<void, ReturnT (ClassT::*)(ArgTs...)>
+    struct fn_object_traits<ReturnT (ClassT::*)(ArgTs...)>
         : function_traits<ReturnT(ArgTs...)> {};
 
     // Specialisation for a const lambda function
     template <typename ReturnT, typename ClassT, typename... ArgTs>
-    struct fn_object_traits<void, ReturnT (ClassT::*)(ArgTs...) const>
+    struct fn_object_traits<ReturnT (ClassT::*)(ArgTs...) const>
         : function_traits<ReturnT(ArgTs...)> {};
 
     // Specialisation for function objects with (non-overloaded) operator()
     // (this includes non-generic lambdas)
     template <typename T>
-    struct fn_traits<decltype(void(&T::operator())), T>
-        : public fn_object_traits<void, decltype(&T::operator())> {};
+    requires requires { &T::operator(); }
+    struct fn_traits<T>
+        : public fn_object_traits<decltype(&T::operator())> {};
 
     // Specialisation for a member function in a non-functor class
     template <typename ReturnT, typename ClassT, typename... ArgTs>
-    struct fn_traits<void, ReturnT (ClassT::*)(ArgTs...)>
+    struct fn_traits<ReturnT (ClassT::*)(ArgTs...)>
         : function_traits<ReturnT(ClassT, ArgTs...)> {};
 
     // Specialisation for a const member function
     template <typename ReturnT, typename ClassT, typename... ArgTs>
-    struct fn_traits<void, ReturnT (ClassT::*)(ArgTs...) const>
+    struct fn_traits<ReturnT (ClassT::*)(ArgTs...) const>
         : function_traits<ReturnT(const ClassT&, ArgTs...)> {};
 
     // Specialisation for a constref member function
     template <typename ReturnT, typename ClassT, typename... ArgTs>
-    struct fn_traits<void, ReturnT (ClassT::*)(ArgTs...) const&>
+    struct fn_traits<ReturnT (ClassT::*)(ArgTs...) const&>
         : function_traits<ReturnT(const ClassT&, ArgTs...)> {};
 
     // Specialisation for a prvalue member function
     template <typename ReturnT, typename ClassT, typename... ArgTs>
-    struct fn_traits<void, ReturnT (ClassT::*)(ArgTs...) &&>
+    struct fn_traits<ReturnT (ClassT::*)(ArgTs...) &&>
         : function_traits<ReturnT(ClassT&&, ArgTs...)> {};
 
     // Specialisation for a pointer-to-member
     template <typename ReturnT, typename ClassT>
-    struct fn_traits<void, ReturnT ClassT::*>
+    struct fn_traits<ReturnT ClassT::*>
         : function_traits<ReturnT&(ClassT)> {};
 
     // Specialisation for a const pointer-to-member
     template <typename ReturnT, typename ClassT>
-    struct fn_traits<void, const ReturnT ClassT::*>
+    struct fn_traits<const ReturnT ClassT::*>
         : function_traits<const ReturnT&(ClassT)> {};
 } // namespace _impl
 
-template <typename FnT>
-using fn_return_t = typename function_traits<FnT>::return_type;
-
 template <typename FnT, int ArgN = 0>
 using fn_arg_t =
     std::tuple_element_t<ArgN, typename function_traits<FnT>::arg_types>;
 
+template <typename FnT>
+constexpr auto fn_arg_count_v =
+    std::tuple_size_v<typename function_traits<FnT>::arg_types>;
+
 } // namespace Quotient