keep_alive call policy (analogous to Boost.Python's with_custodian_and_ward, fixes #62)

example/example13.cpp

@@ -0,0 +1,37 @@
+/*
+    example/example13.cpp -- keep_alive modifier (pybind11's version
+    of Boost.Python's with_custodian_and_ward / with_custodian_and_ward_postcall)
+
+    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"
+
+class Child {
+public:
+    Child() { std::cout << "Allocating child." << std::endl; }
+    ~Child() { std::cout << "Releasing child." << std::endl; }
+};
+
+class Parent {
+public:
+    Parent() { std::cout << "Allocating parent." << std::endl; }
+    ~Parent() { std::cout << "Releasing parent." << std::endl; }
+    void addChild(Child *) { }
+    Child *returnChild() { return new Child(); }
+};
+
+void init_ex13(py::module &m) {
+    py::class_<Parent>(m, "Parent")
+        .def(py::init<>())
+        .def("addChild", &Parent::addChild)
+        .def("addChildKeepAlive", &Parent::addChild, py::keep_alive<1, 2>())
+        .def("returnChild", &Parent::returnChild)
+        .def("returnChildKeepAlive", &Parent::returnChild, py::keep_alive<1, 0>());
+
+    py::class_<Child>(m, "Child")
+        .def(py::init<>());
+}