Simplify visit() signature

Checking that BaseEventT descends from Event is really extraneous.

1 files changed, 12 insertions, 18 deletions

diff --git a/lib/events/event.h b/lib/events/event.h
index 25362786..f985ae92 100644
--- a/lib/events/event.h
+++ b/lib/events/event.h
@@ -334,22 +334,18 @@ inline auto visit(const BaseEventT& event, FnT&& visitor)
     return visitor(event);
 }
 
-template <typename T>
-constexpr auto is_event()
-{
-    return std::is_base_of<Event, std::decay_t<T>>::value;
-}
-
-template <typename T, typename FnT>
-constexpr auto needs_cast()
-{
-    return !std::is_convertible<T, fn_arg_t<FnT>>::value;
+namespace _impl {
+    template <typename T, typename FnT>
+    constexpr auto needs_downcast()
+    {
+        return !std::is_convertible_v<T, fn_arg_t<FnT>>;
+    }
 }
 
 // A single type-specific void visitor
 template <typename BaseEventT, typename FnT>
-inline std::enable_if_t<is_event<BaseEventT>() && needs_cast<BaseEventT, FnT>()
-                        && std::is_void<fn_return_t<FnT>>::value>
+inline std::enable_if_t<_impl::needs_downcast<BaseEventT, FnT>()
+                        && std::is_void_v<fn_return_t<FnT>>>
 visit(const BaseEventT& event, FnT&& visitor)
 {
     using event_type = fn_arg_t<FnT>;
@@ -358,10 +354,9 @@ visit(const BaseEventT& event, FnT&& visitor)
 }
 
 // A single type-specific non-void visitor with an optional default value
+// non-voidness is guarded by defaultValue type
 template <typename BaseEventT, typename FnT>
-inline std::enable_if_t<is_event<BaseEventT>() && needs_cast<BaseEventT, FnT>(),
-                        fn_return_t<FnT>> // non-voidness is guarded by
-                                          // defaultValue type
+inline std::enable_if_t<_impl::needs_downcast<BaseEventT, FnT>(), fn_return_t<FnT>>
 visit(const BaseEventT& event, FnT&& visitor,
       fn_return_t<FnT>&& defaultValue = {})
 {
@@ -373,9 +368,8 @@ visit(const BaseEventT& event, FnT&& visitor,
 
 // A chain of 2 or more visitors
 template <typename BaseEventT, typename FnT1, typename FnT2, typename... FnTs>
-inline std::enable_if_t<is_event<BaseEventT>(), fn_return_t<FnT1>>
-visit(const BaseEventT& event, FnT1&& visitor1, FnT2&& visitor2,
-      FnTs&&... visitors)
+inline fn_return_t<FnT1> visit(const BaseEventT& event, FnT1&& visitor1,
+                               FnT2&& visitor2, FnTs&&... visitors)
 {
     using event_type1 = fn_arg_t<FnT1>;
     if (is<std::decay_t<event_type1>>(event))