From ee1bbedcd98faa2d51437d1bb528b352edd44ed3 Mon Sep 17 00:00:00 2001
From: Volker Hilsheimer <volker.hilsheimer@qt.io>
Date: Sat, 29 Apr 2023 17:08:13 +0200
Subject: [PATCH] Give QtPrivate::List a size value, simplify
 QFunctorSlotObject

The meta-programming list can easily know its size, so no need to pass
both a list and its size as template parameters to QFunctorSlotObject,
which simplifies existing code and is a step towards merging
QFunctorSlotObject and QSlotObject.

Also, remove the unused List_Select helper.

Change-Id: I8ec6a0b707eab531ec06aba4e82223f242e53f2f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/kernel/qobject.h          |  2 +-
 src/corelib/kernel/qobjectdefs_impl.h | 23 ++++++++++++-----------
 src/corelib/kernel/qtimer.h           |  3 +--
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index 7f3720df1f..53c6de654f 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -302,7 +302,7 @@ public:
             types = QtPrivate::ConnectionTypes<typename SignalType::Arguments>::types();
 
         return connectImpl(sender, reinterpret_cast<void **>(&signal), context, nullptr,
-                           new QtPrivate::QFunctorSlotObject<Func2, SlotArgumentCount,
+                           new QtPrivate::QFunctorSlotObject<Func2,
                                 typename QtPrivate::List_Left<typename SignalType::Arguments, SlotArgumentCount>::Value,
                                 typename SignalType::ReturnType>(std::move(slot)),
                            type, types, &SignalType::Object::staticMetaObject);
diff --git a/src/corelib/kernel/qobjectdefs_impl.h b/src/corelib/kernel/qobjectdefs_impl.h
index 8a9254a66d..3951c79fb3 100644
--- a/src/corelib/kernel/qobjectdefs_impl.h
+++ b/src/corelib/kernel/qobjectdefs_impl.h
@@ -29,17 +29,20 @@ namespace QtPrivate {
        the list composed of the first N element of the list
      */
     // With variadic template, lists are represented using a variadic template argument instead of the lisp way
-    template <typename...> struct List {};
-    template <typename Head, typename... Tail> struct List<Head, Tail...> { typedef Head Car; typedef List<Tail...> Cdr; };
+    template <typename... Ts> struct List { static constexpr size_t size = sizeof...(Ts); };
+    template<typename T> struct SizeOfList { static constexpr size_t value = 1; };
+    template<> struct SizeOfList<List<>> { static constexpr size_t value = 0; };
+    template<typename ...Ts> struct SizeOfList<List<Ts...>>  { static constexpr size_t value = List<Ts...>::size; };
+    template <typename Head, typename... Tail> struct List<Head, Tail...> {
+        static constexpr size_t size = 1 + sizeof...(Tail);
+        typedef Head Car; typedef List<Tail...> Cdr;
+    };
     template <typename, typename> struct List_Append;
     template <typename... L1, typename...L2> struct List_Append<List<L1...>, List<L2...>> { typedef List<L1..., L2...> Value; };
     template <typename L, int N> struct List_Left {
         typedef typename List_Append<List<typename L::Car>,typename List_Left<typename L::Cdr, N - 1>::Value>::Value Value;
     };
     template <typename L> struct List_Left<L, 0> { typedef List<> Value; };
-    // List_Select<L,N> returns (via typedef Value) the Nth element of the list L
-    template <typename L, int N> struct List_Select { typedef typename List_Select<typename L::Cdr, N - 1>::Value Value; };
-    template <typename L> struct List_Select<L,0> { typedef typename L::Car Value; };
 
     /*
        trick to set the return value of a slot that works even if the signal or the slot returns void
@@ -418,11 +421,10 @@ namespace QtPrivate {
         explicit QSlotObject(Func f) : QSlotObjectBase(&impl), function(f) {}
     };
     // implementation of QSlotObjectBase for which the slot is a functor (or lambda)
-    // N is the number of arguments
     // Args and R are the List of arguments and the return type of the signal to which the slot is connected.
-    template<typename Func, int N, typename Args, typename R> class QFunctorSlotObject : public QSlotObjectBase
+    template<typename Func, typename Args, typename R> class QFunctorSlotObject : public QSlotObjectBase
     {
-        typedef QtPrivate::Functor<Func, N> FuncType;
+        using FuncType = QtPrivate::Functor<Func, Args::size>;
         Func function;
         static void impl(int which, QSlotObjectBase *this_, QObject *r, void **a, bool *ret)
         {
@@ -449,7 +451,7 @@ namespace QtPrivate {
                                               typename QtPrivate::FunctionPointer<Func>::ReturnType>;
 
     template <typename Func, typename R>
-    using QFunctorSlotObjectWithNoArgs = QFunctorSlotObject<Func, 0, QtPrivate::List<>, R>;
+    using QFunctorSlotObjectWithNoArgs = QFunctorSlotObject<Func, QtPrivate::List<>, R>;
 
     template <typename Func>
     using QFunctorSlotObjectWithNoArgsImplicitReturn = QFunctorSlotObjectWithNoArgs<Func, typename QtPrivate::FunctionPointer<Func>::ReturnType>;
@@ -508,8 +510,7 @@ namespace QtPrivate {
             constexpr int MatchingArgumentCount = QtPrivate::countMatchingArguments<Prototype, Functor>();
             using ActualArguments = typename QtPrivate::List_Left<ExpectedArguments, MatchingArgumentCount>::Value;
 
-            return new QtPrivate::QFunctorSlotObject<Functor, MatchingArgumentCount,
-                                                     ActualArguments, void>(std::move(func));
+            return new QtPrivate::QFunctorSlotObject<Functor,  ActualArguments, void>(std::move(func));
         }
     }
 
diff --git a/src/corelib/kernel/qtimer.h b/src/corelib/kernel/qtimer.h
index 5599b60bd7..a58eafa7d3 100644
--- a/src/corelib/kernel/qtimer.h
+++ b/src/corelib/kernel/qtimer.h
@@ -121,8 +121,7 @@ public:
         static_assert(int(SlotType::ArgumentCount) <= 0,  "The slot must not have any arguments.");
 
         singleShotImpl(interval, timerType, context,
-                       new QtPrivate::QFunctorSlotObject<Func1, 0,
-                            typename QtPrivate::List_Left<void, 0>::Value, void>(std::move(slot)));
+                       new QtPrivate::QFunctorSlotObject<Func1, QtPrivate::List<>, void>(std::move(slot)));
     }
 
     template <typename ... Args>