From 1fafd1b44796f39e56d4c029203c0e2ba18a60dd Mon Sep 17 00:00:00 2001
From: Henry Schreiner <henryschreineriii@gmail.com>
Date: Fri, 6 Aug 2021 13:03:26 -0400
Subject: [PATCH] fix: apply simpler expression with fewer workarounds

---
 include/pybind11/detail/type_caster_base.h | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/include/pybind11/detail/type_caster_base.h b/include/pybind11/detail/type_caster_base.h
index e2d1bcb8..a708d87f 100644
--- a/include/pybind11/detail/type_caster_base.h
+++ b/include/pybind11/detail/type_caster_base.h
@@ -927,18 +927,17 @@ protected:
     using Constructor = void *(*)(const void *);
 
     /* Only enabled when the types are {copy,move}-constructible *and* when the type
-       does not have a private operator new implementation. */
+       does not have a private operator new implementation. A comma operator is used in the decltype
+       argument to apply SFINAE to the public copy/move constructors.*/
     template <typename T, typename = enable_if_t<is_copy_constructible<T>::value>>
-    static auto make_copy_constructor(const T *x) -> decltype(new T(*x), Constructor{}) {
-        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(x);
+    static auto make_copy_constructor(const T *) -> decltype(new T(std::declval<const T>()), Constructor{}) {
         return [](const void *arg) -> void * {
             return new T(*reinterpret_cast<const T *>(arg));
         };
     }
 
     template <typename T, typename = enable_if_t<std::is_move_constructible<T>::value>>
-    static auto make_move_constructor(const T *x) -> decltype(new T(std::move(*const_cast<T *>(x))), Constructor{}) {
-        PYBIND11_WORKAROUND_INCORRECT_MSVC_C4100(x);
+    static auto make_move_constructor(const T *) -> decltype(new T(std::declval<T&&>()), Constructor{}) {
         return [](const void *arg) -> void * {
             return new T(std::move(*const_cast<T *>(reinterpret_cast<const T *>(arg))));
         };