return best representation of polymorphic types (fixes #105)

CMakeLists.txt

@@ -121,6 +121,7 @@ set(PYBIND11_EXAMPLES
   example/example13.cpp
   example/example14.cpp
   example/example15.cpp
+  example/example16.cpp
   example/issues.cpp
 )
 

docs/changelog.rst

@@ -5,7 +5,8 @@ Changelog
 
 1.5 (not yet released)
 ----------------------
-* Pickling support
+* For polymorphic types, use RTTI to try to return the closest type registered with pybind11.
+* Pickling support for serializing and unserializing C++ instances to a byte stream in Python
 * Added a variadic ``make_tuple()`` function
 * Address a rare issue that could confuse the current virtual function dispatcher
 * Documentation improvements: import issues, symbol visibility, pickling, limitations

example/example.cpp

@@ -24,6 +24,7 @@ void init_ex12(py::module &);
 void init_ex13(py::module &);
 void init_ex14(py::module &);
 void init_ex15(py::module &);
+void init_ex16(py::module &);
 void init_issues(py::module &);
 
 PYBIND11_PLUGIN(example) {
@@ -44,6 +45,7 @@ PYBIND11_PLUGIN(example) {
     init_ex13(m);
     init_ex14(m);
     init_ex15(m);
+    init_ex16(m);
     init_issues(m);
 
     return m.ptr();

example/example16.cpp

+/*
+    example/example16.cpp -- automatic upcasting for polymorphic types
+
+    Copyright (c) 2015 Wenzel Jakob <wenzel@inf.ethz.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#include "example.h"
+
+struct BaseClass { virtual ~BaseClass() {} };
+struct DerivedClass1 : BaseClass { };
+struct DerivedClass2 : BaseClass { };
+
+void init_ex16(py::module &m) {
+    py::class_<BaseClass>(m, "BaseClass").def(py::init<>());
+    py::class_<DerivedClass1>(m, "DerivedClass1").def(py::init<>());
+    py::class_<DerivedClass2>(m, "DerivedClass2").def(py::init<>());
+
+    m.def("return_class_1", []() -> BaseClass* { return new DerivedClass1(); });
+    m.def("return_class_2", []() -> BaseClass* { return new DerivedClass2(); });
+    m.def("return_none", []() -> BaseClass* { return nullptr; });
+}

example/example16.py

+from __future__ import print_function
+import sys
+
+sys.path.append('.')
+
+from example import return_class_1
+from example import return_class_2
+from example import return_none
+
+print(type(return_class_1()))
+print(type(return_class_2()))
+print(type(return_none()))

example/example16.ref

+<class 'example.DerivedClass1'>
+<class 'example.DerivedClass2'>
+<type 'NoneType'>

include/pybind11/cast.h

@@ -137,6 +137,7 @@ public:
 
     PYBIND11_NOINLINE static handle cast(const void *_src, return_value_policy policy, handle parent,
                                          const std::type_info *type_info,
+                                         const std::type_info *type_info_backup,
                                          void *(*copy_constructor)(const void *),
                                          const void *existing_holder = nullptr) {
         void *src = const_cast<void *>(_src);
@@ -154,6 +155,11 @@ public:
 
         auto it = internals.registered_types_cpp.find(std::type_index(*type_info));
         if (it == internals.registered_types_cpp.end()) {
+            type_info = type_info_backup;
+            it = internals.registered_types_cpp.find(std::type_index(*type_info));
+        }
+
+        if (it == internals.registered_types_cpp.end()) {
             std::string tname = type_info->name();
             detail::clean_type_id(tname);
             std::string msg = "Unregistered type : " + tname;
@@ -213,11 +219,11 @@ public:
     static handle cast(const type &src, return_value_policy policy, handle parent) {
         if (policy == return_value_policy::automatic)
             policy = return_value_policy::copy;
-        return type_caster_generic::cast(&src, policy, parent, &typeid(type), &copy_constructor);
+        return cast(&src, policy, parent);
     }
 
     static handle cast(const type *src, return_value_policy policy, handle parent) {
-        return type_caster_generic::cast(src, policy, parent, &typeid(type), &copy_constructor);
+        return type_caster_generic::cast(src, policy, parent, src ? &typeid(*src) : nullptr, &typeid(type), &copy_constructor);
     }
 
     template <typename T> using cast_op_type = pybind11::detail::cast_op_type<T>;
@@ -664,7 +670,9 @@ public:
 
     static handle cast(const holder_type &src, return_value_policy policy, handle parent) {
         return type_caster_generic::cast(
-            src.get(), policy, parent, &typeid(type), &copy_constructor, &src);
+            src.get(), policy, parent,
+            src.get() ? &typeid(*src.get()) : nullptr, &typeid(type),
+            &copy_constructor, &src);
     }
 
 protected: