Initialize prop_id_ in NPyMechObj.

src/nrnpython/nrnpy_nrn.cpp

@@ -55,19 +55,21 @@
     PyObject_HEAD
     NPySegObj* pyseg_;
     Prop* prop_;
-    neuron::container::non_owning_identifier_without_container prop_id_{};
+    // Following cannot be initialized when NPyMechObj allocated by Python. See new_pymechobj
+    // wrapper.
+    neuron::container::non_owning_identifier_without_container prop_id_;
     int type_;
 } NPyMechObj;
 
 typedef struct {
     PyObject_HEAD
-    NPyMechObj* pymech_{};
+    NPyMechObj* pymech_;
 } NPyMechOfSegIter;
 
 typedef struct {
     PyObject_HEAD
-    NPyMechObj* pymech_{};
-    NPyDirectMechFunc* f_{};
+    NPyMechObj* pymech_;
+    NPyDirectMechFunc* f_;
 } NPyMechFunc;
 
 typedef struct {
@@ -257,12 +259,26 @@
 static void NPyMechObj_dealloc(NPyMechObj* self) {
     // printf("NPyMechObj_dealloc %p %s\n", self, self->ob_type->tp_name);
     Py_XDECREF(self->pyseg_);
+    // Must manually call destructor since it was manually constructed in new_pymechobj wrapper
+    self->prop_id_.~non_owning_identifier_without_container();
     ((PyObject*) self)->ob_type->tp_free((PyObject*) self);
 }
 
+static NPyMechObj* new_pymechobj() {
+    NPyMechObj* m = PyObject_New(NPyMechObj, pmech_generic_type);
+    if (m) {
+        // Use "placement new" idiom since Python C allocation cannot call the initializer to start
+        // it as "null". So later `a = b` might segfault because copy constructor decrements the
+        // refcount of `a`s nonsense memory.
+        new (&m->prop_id_) neuron::container::non_owning_identifier_without_container;
+    }
+
+    return m;
+}
+
 // Only call if p is valid
 static NPyMechObj* new_pymechobj(NPySegObj* pyseg, Prop* p) {
-    NPyMechObj* m = PyObject_New(NPyMechObj, pmech_generic_type);
+    NPyMechObj* m = new_pymechobj();
     if (!m) {
         return NULL;
     }
@@ -436,6 +452,7 @@
     // printf("NPyMechObj_new %p %s\n", self,
     // ((PyObject*)self)->ob_type->tp_name);
     if (self != NULL) {
+        new (self) NPyMechObj;
         self->pyseg_ = pyseg;
         Py_INCREF(self->pyseg_);
     }
@@ -1669,7 +1686,7 @@
     if (!r) {
         return NULL;
     }
-    r->pymech_ = PyObject_New(NPyMechObj, pmech_generic_type);
+    r->pymech_ = new_pymechobj();
     r->pymech_->pyseg_ = PyObject_New(NPySegObj, psegment_type);
     r->pymech_->pyseg_->pysec_ = sec;
     Py_INCREF(sec);
@@ -1916,7 +1933,7 @@
         sym = ((NPyRangeVar*) rv)->sym_;
         if (ISARRAY(sym)) {
             NPyRangeVar* r = PyObject_New(NPyRangeVar, range_type);
-            r->pymech_ = PyObject_New(NPyMechObj, pmech_generic_type);
+            r->pymech_ = new_pymechobj();
             r->pymech_->pyseg_ = self;
             Py_INCREF(r->pymech_->pyseg_);
             r->sym_ = sym;
@@ -1944,7 +1961,7 @@
                    sym->type == RANGEVAR) {
             if (ISARRAY(sym)) {
                 NPyRangeVar* r = PyObject_New(NPyRangeVar, range_type);
-                r->pymech_ = PyObject_New(NPyMechObj, pmech_generic_type);
+                r->pymech_ = new_pymechobj();
                 r->pymech_->pyseg_ = self;
                 Py_INCREF(self);
                 r->sym_ = sym;