Modernize Tuple Protocol implementations

The existing get<I>() implementations are very clever™, if I, as their
inventor in at least the Qt ecosystem, may say so myself. E.g. the ()
around the return value are absolutely required, to ensure we return
by reference, not by value, through decltype(auto).

C++23 gives us forward_like, which doesn't require the parentheses,
because it always returns a reference.

Also replace decay_t with C++20's remove_cvref_t, the latter being
more efficient (performs less work).

Change-Id: Ic9ed0c25e6d6bfbd77d7c85858a8d97fe58be615
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/src/gui/math3d/qvectornd.h b/src/gui/math3d/qvectornd.h
index 0f3ce758a8..639b8f0e5a 100644
--- a/src/gui/math3d/qvectornd.h
+++ b/src/gui/math3d/qvectornd.h
@@ -10,6 +10,9 @@
 #include <QtCore/qrect.h>
 #include <QtCore/qmath.h>
 
+#include <QtCore/q20type_traits.h>
+#include <QtCore/q23utility.h>
+
 QT_BEGIN_NAMESPACE
 
 class QVector2D;
@@ -145,10 +148,10 @@ private:
     template <std::size_t I,
               typename V,
               std::enable_if_t<(I < 2), bool> = true,
-              std::enable_if_t<std::is_same_v<std::decay_t<V>, QVector2D>, bool> = true>
+              std::enable_if_t<std::is_same_v<q20::remove_cvref_t<V>, QVector2D>, bool> = true>
     friend constexpr decltype(auto) get(V &&vec) noexcept
     {
-        return (std::forward<V>(vec).v[I]);
+        return q23::forward_like<V>(vec.v[I]);
     }
 };
 
@@ -304,10 +307,10 @@ private:
     template <std::size_t I,
               typename V,
               std::enable_if_t<(I < 3), bool> = true,
-              std::enable_if_t<std::is_same_v<std::decay_t<V>, QVector3D>, bool> = true>
+              std::enable_if_t<std::is_same_v<q20::remove_cvref_t<V>, QVector3D>, bool> = true>
     friend constexpr decltype(auto) get(V &&vec) noexcept
     {
-        return (std::forward<V>(vec).v[I]);
+        return q23::forward_like<V>(vec.v[I]);
     }
 };
 
@@ -456,10 +459,10 @@ private:
     template <std::size_t I,
               typename V,
               std::enable_if_t<(I < 4), bool> = true,
-              std::enable_if_t<std::is_same_v<std::decay_t<V>, QVector4D>, bool> = true>
+              std::enable_if_t<std::is_same_v<q20::remove_cvref_t<V>, QVector4D>, bool> = true>
     friend constexpr decltype(auto) get(V &&vec) noexcept
     {
-        return (std::forward<V>(vec).v[I]);
+        return q23::forward_like<V>(vec.v[I]);
     }
 };