JNI: simplify implementation of native function wrappers

When declaring native callback functions with the JNI type system, then
we actually register a helper function with variadic arguments, and
implement that to forward the arguments to the declared function, which
then might use higher-level types as arguments. We deduce those
higher-level types through a variadic template, and use std::tuple as
well as std::apply to generate the calls.

Simplify the implementation by using std::make_tuple, and replace
q20:remove_cvref_t with std::decay_t; this is what std::make_tuple uses,
and we don't need to maintain functions and arrays as such.

Found during 6.7 header review.

Pick-to: 6.7
Task-number: QTBUG-119952
Change-Id: I7cd206c6b372c2ec62a10feb5f9253f5607f01a9
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

1 files changed, 3 insertions, 5 deletions

diff --git a/src/corelib/kernel/qjnitypes.h b/src/corelib/kernel/qjnitypes.h
index 56af657fa3..71c4db670c 100644
--- a/src/corelib/kernel/qjnitypes.h
+++ b/src/corelib/kernel/qjnitypes.h
@@ -96,20 +96,18 @@ struct JNITypeForArgImpl<QString>
 };
 
 template <typename Arg>
-using JNITypeForArg = typename JNITypeForArgImpl<q20::remove_cvref_t<Arg>>::Type;
+using JNITypeForArg = typename JNITypeForArgImpl<std::decay_t<Arg>>::Type;
 template <typename Arg, typename Type>
 static inline auto methodArgFromVarArg(Type &&t)
 {
-    return JNITypeForArgImpl<q20::remove_cvref_t<Arg>>::fromVarArg(std::move(t));
+    return JNITypeForArgImpl<std::decay_t<Arg>>::fromVarArg(std::move(t));
 }
 
 // Turn a va_list into a tuple of typed arguments
 template <typename ...Args>
 static constexpr auto makeTupleFromArgsHelper(va_list args)
 {
-    return std::tuple<q20::remove_cvref_t<Args>...>{
-        methodArgFromVarArg<q20::remove_cvref_t<Args>>(va_arg(args, JNITypeForArg<Args>))...
-    };
+    return std::tuple(methodArgFromVarArg<Args>(va_arg(args, JNITypeForArg<Args>))...);
 }
 
 template <typename Ret, typename ...Args>