From 74ac0d99fb5c70aa66248fed5d7536089da3e253 Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Mon, 9 Oct 2023 05:08:24 -0700
Subject: [PATCH] Revert "Go back to using `union` as originally suggested by
 jbms@. The trick (also suggested by jbms@) is to add empty ctor + dtor."

This reverts commit e7b8c4f0fcd72191e88d1c17abf5da08fe3a9c6f.
---
 include/pybind11/numpy.h | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/include/pybind11/numpy.h b/include/pybind11/numpy.h
index 0a00120c9..5a60f18b2 100644
--- a/include/pybind11/numpy.h
+++ b/include/pybind11/numpy.h
@@ -21,6 +21,7 @@
 #include <functional>
 #include <numeric>
 #include <sstream>
+#include <stdalign.h>
 #include <string>
 #include <type_traits>
 #include <typeindex>
@@ -54,21 +55,16 @@ public:
             // Multiple threads may run this concurrently, but that is fine.
             auto value = initialize(); // May release and re-acquire the GIL.
             if (!initialized_) {       // This runs with the GIL held,
-                new (&value_)          // therefore this is reached only once.
-                    T(std::move(value));
+                new                    // therefore this is reached only once.
+                    (reinterpret_cast<T *>(value_storage_)) T(std::move(value));
                 initialized_ = true;
             }
         }
-        return value_;
+        return *reinterpret_cast<T *>(value_storage_);
     }
 
-    LazyInitializeAtLeastOnceDestroyNever() {}
-    ~LazyInitializeAtLeastOnceDestroyNever() {}
-
 private:
-    union {
-        T value_;
-    };
+    alignas(T) char value_storage_[sizeof(T)];
     bool initialized_ = false;
 };