improved shared pointer support (fixes #14)

Author: Wenzel Jakob

docs/advanced.rst

@@ -457,6 +457,14 @@ be declared at the top level before any binding code:
     demonstrates how to work with custom reference-counting holder types in
     more detail.
 
+.. warning::
+
+   To ensure correct reference counting among Python and C++, the use of
+   ``std::shared_ptr<T>`` as a holder type requires that ``T`` inherits from
+   ``std::enable_shared_from_this<T>`` (see cppreference_ for details).
+
+.. _cppreference: http://en.cppreference.com/w/cpp/memory/enable_shared_from_this
+
 .. _custom_constructors:
 
 Custom constructors

example/example8.cpp

@@ -31,14 +31,36 @@ class MyObject : public Object {
     int value;
 };
 
+class MyObject2 : public std::enable_shared_from_this<MyObject2> {
+public:
+    MyObject2(int value) : value(value) {
+        std::cout << toString() << " constructor" << std::endl;
+    }
+
+    std::string toString() const {
+        return "MyObject2[" + std::to_string(value) + "]";
+    }
+
+    virtual ~MyObject2() {
+        std::cout << toString() << " destructor" << std::endl;
+    }
+
+private:
+    int value;
+};
+
 /// Make pybind aware of the ref-counted wrapper type
 PYBIND11_DECLARE_HOLDER_TYPE(T, ref<T>);
+PYBIND11_DECLARE_HOLDER_TYPE(T, std::shared_ptr<T>);
 
 Object *make_object_1() { return new MyObject(1); }
 ref<Object> make_object_2() { return new MyObject(2); }
 MyObject *make_myobject_4() { return new MyObject(4); }
 ref<MyObject> make_myobject_5() { return new MyObject(5); }
 
+MyObject2 *make_myobject2_1() { return new MyObject2(1); }
+std::shared_ptr<MyObject2> make_myobject2_2() { return std::make_shared<MyObject2>(2); }
+
 void print_object_1(const Object *obj) { std::cout << obj->toString() << std::endl; }
 void print_object_2(ref<Object> obj) { std::cout << obj->toString() << std::endl; }
 void print_object_3(const ref<Object> &obj) { std::cout << obj->toString() << std::endl; }
@@ -49,6 +71,11 @@ void print_myobject_2(ref<MyObject> obj) { std::cout << obj->toString() << std::
 void print_myobject_3(const ref<MyObject> &obj) { std::cout << obj->toString() << std::endl; }
 void print_myobject_4(const ref<MyObject> *obj) { std::cout << (*obj)->toString() << std::endl; }
 
+void print_myobject2_1(const MyObject2 *obj) { std::cout << obj->toString() << std::endl; }
+void print_myobject2_2(std::shared_ptr<MyObject2> obj) { std::cout << obj->toString() << std::endl; }
+void print_myobject2_3(const std::shared_ptr<MyObject2> &obj) { std::cout << obj->toString() << std::endl; }
+void print_myobject2_4(const std::shared_ptr<MyObject2> *obj) { std::cout << (*obj)->toString() << std::endl; }
+
 void init_ex8(py::module &m) {
     py::class_<Object, ref<Object>> obj(m, "Object");
     obj.def("getRefCount", &Object::getRefCount);
@@ -69,5 +96,14 @@ void init_ex8(py::module &m) {
     m.def("print_myobject_3", &print_myobject_3);
     m.def("print_myobject_4", &print_myobject_4);
 
+    py::class_<MyObject2, std::shared_ptr<MyObject2>>(m, "MyObject2")
+        .def(py::init<int>());
+    m.def("make_myobject2_1", &make_myobject2_1);
+    m.def("make_myobject2_2", &make_myobject2_2);
+    m.def("print_myobject2_1", &print_myobject2_1);
+    m.def("print_myobject2_2", &print_myobject2_2);
+    m.def("print_myobject2_3", &print_myobject2_3);
+    m.def("print_myobject2_4", &print_myobject2_4);
+
     py::implicitly_convertible<py::int_, MyObject>();
 }

example/example8.py

@@ -8,6 +8,8 @@
 from example import make_object_2
 from example import make_myobject_4
 from example import make_myobject_5
+from example import make_myobject2_1
+from example import make_myobject2_2
 from example import print_object_1
 from example import print_object_2
 from example import print_object_3
@@ -16,6 +18,10 @@
 from example import print_myobject_2
 from example import print_myobject_3
 from example import print_myobject_4
+from example import print_myobject2_1
+from example import print_myobject2_2
+from example import print_myobject2_3
+from example import print_myobject2_4
 
 for o in [make_object_1(), make_object_2(), MyObject(3)]:
     print("Reference count = %i" % o.getRefCount())
@@ -35,3 +41,11 @@
     print_myobject_2(o)
     print_myobject_3(o)
     print_myobject_4(o)
+
+
+for o in [make_myobject2_1(), make_myobject2_2()]:
+    print(o)
+    print_myobject2_1(o)
+    print_myobject2_2(o)
+    print_myobject2_3(o)
+    print_myobject2_4(o)