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

example/example.cpp

@@ -21,6 +21,7 @@ void init_ex9(py::module &);
 void init_ex10(py::module &);
 void init_ex11(py::module &);
 void init_ex12(py::module &);
+void init_ex13(py::module &);
 
 PYBIND11_PLUGIN(example) {
     py::module m("example", "pybind example plugin");
@@ -37,6 +38,7 @@ PYBIND11_PLUGIN(example) {
     init_ex10(m);
     init_ex11(m);
     init_ex12(m);
+    init_ex13(m);
 
     return m.ptr();
 }

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<>());
+}

example/example13.py

@@ -0,0 +1,46 @@
+from __future__ import print_function
+import sys
+import gc
+sys.path.append('.')
+
+from example import Parent, Child
+
+if True:
+    p = Parent()
+    p.addChild(Child())
+    gc.collect()
+    print(p)
+    p = None
+
+gc.collect()
+print("")
+
+if True:
+    p = Parent()
+    p.returnChild()
+    gc.collect()
+    print(p)
+    p = None
+
+gc.collect()
+print("")
+
+if True:
+    p = Parent()
+    p.addChildKeepAlive(Child())
+    gc.collect()
+    print(p)
+    p = None
+gc.collect()
+print("")
+
+if True:
+    p = Parent()
+    p.returnChildKeepAlive()
+    gc.collect()
+    print(p)
+    p = None
+
+gc.collect()
+print("")
+print("Terminating..")

example/example13.ref

@@ -0,0 +1,25 @@
+Allocating parent.
+Allocating child.
+Releasing child.
+<example.Parent object at 0x10eb726c0>
+Releasing parent.
+
+Allocating parent.
+Allocating child.
+Releasing child.
+<example.Parent object at 0x10eb726c0>
+Releasing parent.
+
+Allocating parent.
+Allocating child.
+<example.Parent object at 0x10eb726c0>
+Releasing parent.
+Releasing child.
+
+Allocating parent.
+Allocating child.
+<example.Parent object at 0x10eb726c0>
+Releasing parent.
+Releasing child.
+
+Terminating..