From 5b5253ba2f8697d8b96decea80742258bf3ce0bb Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Mon, 12 Aug 2024 08:27:21 -0600
Subject: [PATCH] Disallow copying SmartPointers pointing to dead objects.

---
 include/deal.II/base/smartpointer.h | 37 ++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/include/deal.II/base/smartpointer.h b/include/deal.II/base/smartpointer.h
index 73728ca047..5e39ead3f8 100644
--- a/include/deal.II/base/smartpointer.h
+++ b/include/deal.II/base/smartpointer.h
@@ -305,8 +305,13 @@ inline SmartPointer<T, P>::SmartPointer(const SmartPointer<T, Q> &tt)
   , id(tt.id)
   , pointed_to_object_is_alive(false)
 {
-  if (tt.pointed_to_object_is_alive && t != nullptr)
-    t->subscribe(&pointed_to_object_is_alive, id);
+  if (tt != nullptr)
+    {
+      Assert(tt.pointed_to_object_is_alive,
+             ExcMessage("You can't copy a smart pointer object that "
+                        "is pointing to an object that is no longer alive."));
+      t->subscribe(&pointed_to_object_is_alive, id);
+    }
 }
 
 
@@ -317,8 +322,13 @@ inline SmartPointer<T, P>::SmartPointer(const SmartPointer<T, P> &tt)
   , id(tt.id)
   , pointed_to_object_is_alive(false)
 {
-  if (tt.pointed_to_object_is_alive && t != nullptr)
-    t->subscribe(&pointed_to_object_is_alive, id);
+  if (tt != nullptr)
+    {
+      Assert(tt.pointed_to_object_is_alive,
+             ExcMessage("You can't copy a smart pointer object that "
+                        "is pointing to an object that is no longer alive."));
+      t->subscribe(&pointed_to_object_is_alive, id);
+    }
 }
 
 
@@ -419,8 +429,13 @@ SmartPointer<T, P>::operator=(const SmartPointer<T, Q> &tt)
 
   // Then reset to the new object, and subscribe to it
   t = (tt != nullptr ? tt.get() : nullptr);
-  if (tt.pointed_to_object_is_alive && tt != nullptr)
-    t->subscribe(&pointed_to_object_is_alive, id);
+  if (tt != nullptr)
+    {
+      Assert(tt.pointed_to_object_is_alive,
+             ExcMessage("You can't copy a smart pointer object that "
+                        "is pointing to an object that is no longer alive."));
+      t->subscribe(&pointed_to_object_is_alive, id);
+    }
   return *this;
 }
 
@@ -442,9 +457,13 @@ SmartPointer<T, P>::operator=(const SmartPointer<T, P> &tt)
 
   // Then reset to the new object, and subscribe to it
   t = (tt != nullptr ? tt.get() : nullptr);
-  if (tt.pointed_to_object_is_alive && tt != nullptr)
-    t->subscribe(&pointed_to_object_is_alive, id);
-
+  if (tt != nullptr)
+    {
+      Assert(tt.pointed_to_object_is_alive,
+             ExcMessage("You can't copy a smart pointer object that "
+                        "is pointing to an object that is no longer alive."));
+      t->subscribe(&pointed_to_object_is_alive, id);
+    }
   return *this;
 }
 
-- 
2.39.5