Merge pull request #437 from dean0x7d/dynamic-attrs

Add dynamic attribute support

include/pybind11/attr.h

@@ -44,6 +44,9 @@ template <int Nurse, int Patient> struct keep_alive { };
 /// Annotation indicating that a class is involved in a multiple inheritance relationship
 struct multiple_inheritance { };
 
+/// Annotation which enables dynamic attributes, i.e. adds `__dict__` to a class
+struct dynamic_attr { };
+
 NAMESPACE_BEGIN(detail)
 /* Forward declarations */
 enum op_id : int;
@@ -162,6 +165,9 @@ struct type_record {
     /// Multiple inheritance marker
     bool multiple_inheritance = false;
 
+    /// Does the class manage a __dict__?
+    bool dynamic_attr = false;
+
     PYBIND11_NOINLINE void add_base(const std::type_info *base, void *(*caster)(void *)) {
         auto base_info = detail::get_type_info(*base, false);
         if (!base_info) {
@@ -292,6 +298,11 @@ struct process_attribute<multiple_inheritance> : process_attribute_default<multi
     static void init(const multiple_inheritance &, type_record *r) { r->multiple_inheritance = true; }
 };
 
+template <>
+struct process_attribute<dynamic_attr> : process_attribute_default<dynamic_attr> {
+    static void init(const dynamic_attr &, type_record *r) { r->dynamic_attr = true; }
+};
+
 /***
  * Process a keep_alive call policy -- invokes keep_alive_impl during the
  * pre-call handler if both Nurse, Patient != 0 and use the post-call handler

include/pybind11/pybind11.h

@@ -573,6 +573,33 @@ public:
 };
 
 NAMESPACE_BEGIN(detail)
+extern "C" inline PyObject *get_dict(PyObject *op, void *) {
+    PyObject *&dict = *_PyObject_GetDictPtr(op);
+    if (!dict) {
+        dict = PyDict_New();
+    }
+    Py_XINCREF(dict);
+    return dict;
+}
+
+extern "C" inline int set_dict(PyObject *op, PyObject *new_dict, void *) {
+    if (!PyDict_Check(new_dict)) {
+        PyErr_Format(PyExc_TypeError, "__dict__ must be set to a dictionary, not a '%.200s'",
+                     Py_TYPE(new_dict)->tp_name);
+        return -1;
+    }
+    PyObject *&dict = *_PyObject_GetDictPtr(op);
+    Py_INCREF(new_dict);
+    Py_CLEAR(dict);
+    dict = new_dict;
+    return 0;
+}
+
+static PyGetSetDef generic_getset[] = {
+    {const_cast<char*>("__dict__"), get_dict, set_dict, nullptr, nullptr},
+    {nullptr, nullptr, nullptr, nullptr, nullptr}
+};
+
 /// Generic support for creating new Python heap types
 class generic_type : public object {
     template <typename...> friend class class_;
@@ -684,6 +711,16 @@ protected:
 #endif
         type->ht_type.tp_flags &= ~Py_TPFLAGS_HAVE_GC;
 
+        /* Support dynamic attributes */
+        if (rec->dynamic_attr) {
+            type->ht_type.tp_flags |= Py_TPFLAGS_HAVE_GC;
+            type->ht_type.tp_dictoffset = type->ht_type.tp_basicsize; // place the dict at the end
+            type->ht_type.tp_basicsize += sizeof(PyObject *); // and allocate enough space for it
+            type->ht_type.tp_getset = generic_getset;
+            type->ht_type.tp_traverse = traverse;
+            type->ht_type.tp_clear = clear;
+        }
+
         type->ht_type.tp_doc = tp_doc;
 
         if (PyType_Ready(&type->ht_type) < 0)
@@ -785,10 +822,27 @@ protected:
 
             if (self->weakrefs)
                 PyObject_ClearWeakRefs((PyObject *) self);
+
+            PyObject **dict_ptr = _PyObject_GetDictPtr((PyObject *) self);
+            if (dict_ptr) {
+                Py_CLEAR(*dict_ptr);
+            }
         }
         Py_TYPE(self)->tp_free((PyObject*) self);
     }
 
+    static int traverse(PyObject *op, visitproc visit, void *arg) {
+        PyObject *&dict = *_PyObject_GetDictPtr(op);
+        Py_VISIT(dict);
+        return 0;
+    }
+
+    static int clear(PyObject *op) {
+        PyObject *&dict = *_PyObject_GetDictPtr(op);
+        Py_CLEAR(dict);
+        return 0;
+    }
+
     void install_buffer_funcs(
             buffer_info *(*get_buffer)(PyObject *, void *),
             void *get_buffer_data) {