From 639f1d482633a7adb72164c56e3b5ea429db96a5 Mon Sep 17 00:00:00 2001
From: Kitsune Ral <Kitsune-Ral@users.sf.net>
Date: Sun, 27 Dec 2020 23:19:12 +0100
Subject: event.h: Minor tweaks around visit<>

---
 lib/events/event.h | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/lib/events/event.h b/lib/events/event.h
index 626a0229..309ebddf 100644
--- a/lib/events/event.h
+++ b/lib/events/event.h
@@ -298,7 +298,7 @@ using Events = EventsArray<Event>;
 
 // === is<>(), eventCast<>() and visit<>() ===
 
-template <typename EventT>
+template <class EventT>
 inline bool is(const Event& e)
 {
     return e.type() == typeId<EventT>();
@@ -309,7 +309,7 @@ inline bool isUnknown(const Event& e)
     return e.type() == unknownEventTypeId();
 }
 
-template <typename EventT, typename BasePtrT>
+template <class EventT, typename BasePtrT>
 inline auto eventCast(const BasePtrT& eptr)
     -> decltype(static_cast<EventT*>(&*eptr))
 {
@@ -319,7 +319,7 @@ inline auto eventCast(const BasePtrT& eptr)
 }
 
 // A single generic catch-all visitor
-template <typename BaseEventT, typename FnT>
+template <class BaseEventT, typename FnT>
 inline auto visit(const BaseEventT& event, FnT&& visitor)
     -> decltype(visitor(event))
 {
@@ -327,18 +327,17 @@ inline auto visit(const BaseEventT& event, FnT&& visitor)
 }
 
 namespace _impl {
-    template <typename T, typename FnT>
-    constexpr auto needs_downcast()
-    {
-        return !std::is_convertible_v<T, fn_arg_t<FnT>>;
-    }
+    template <class BaseT, typename FnT>
+    inline constexpr auto needs_downcast =
+        std::is_base_of_v<BaseT, std::decay_t<fn_arg_t<FnT>>>
+        && !std::is_same_v<BaseT, std::decay_t<fn_arg_t<FnT>>>;
 }
 
 // A single type-specific void visitor
-template <typename BaseEventT, typename FnT>
-inline std::enable_if_t<_impl::needs_downcast<BaseEventT, FnT>()
+template <class BaseT, typename FnT>
+inline auto visit(const BaseT& event, FnT&& visitor)
+    -> std::enable_if_t<_impl::needs_downcast<BaseT, FnT>
                         && std::is_void_v<fn_return_t<FnT>>>
-visit(const BaseEventT& event, FnT&& visitor)
 {
     using event_type = fn_arg_t<FnT>;
     if (is<std::decay_t<event_type>>(event))
@@ -347,10 +346,10 @@ 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<_impl::needs_downcast<BaseEventT, FnT>(), fn_return_t<FnT>>
-visit(const BaseEventT& event, FnT&& visitor,
-      fn_return_t<FnT>&& defaultValue = {})
+template <class BaseT, typename FnT>
+inline auto visit(const BaseT& event, FnT&& visitor,
+                  fn_return_t<FnT>&& defaultValue = {})
+    -> std::enable_if_t<_impl::needs_downcast<BaseT, FnT>, fn_return_t<FnT>>
 {
     using event_type = fn_arg_t<FnT>;
     if (is<std::decay_t<event_type>>(event))
@@ -359,9 +358,10 @@ visit(const BaseEventT& event, FnT&& visitor,
 }
 
 // A chain of 2 or more visitors
-template <typename BaseEventT, typename FnT1, typename FnT2, typename... FnTs>
-inline fn_return_t<FnT1> visit(const BaseEventT& event, FnT1&& visitor1,
-                               FnT2&& visitor2, FnTs&&... visitors)
+template <class BaseT, typename FnT1, typename FnT2, typename... FnTs>
+inline std::common_type_t<fn_return_t<FnT1>, fn_return_t<FnT2>> visit(
+        const BaseT& event, FnT1&& visitor1, FnT2&& visitor2,
+        FnTs&&... visitors)
 {
     using event_type1 = fn_arg_t<FnT1>;
     if (is<std::decay_t<event_type1>>(event))
@@ -374,8 +374,8 @@ inline fn_return_t<FnT1> visit(const BaseEventT& event, FnT1&& visitor1,
 // over a range of event pointers
 template <typename RangeT, typename... FnTs>
 inline auto visitEach(RangeT&& events, FnTs&&... visitors)
-    -> std::enable_if_t<std::is_convertible_v<
-                            std::decay_t<decltype(**events.begin())>, Event>>
+    -> std::enable_if_t<std::is_void_v<
+            decltype(visit(**begin(events), std::forward<FnTs>(visitors)...))>>
 {
     for (auto&& evtPtr: events)
         visit(*evtPtr, std::forward<FnTs>(visitors)...);
-- 
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