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Title: added 'construct_custodian_for' and test by ukoethe · Pull Request #8 · boostorg/python · GitHub

Open Graph Title: added 'construct_custodian_for' and test by ukoethe · Pull Request #8 · boostorg/python

X Title: added 'construct_custodian_for' and test by ukoethe · Pull Request #8 · boostorg/python

Description: (note: I will update the documentation as well when this pull request gets accepted) This pull request proposes a fix for the long-standing problem that with_custodian_and_ward_postcall doesn't work in connection with make_constructor (see e.g. https://mail.python.org/pipermail/cplusplus-sig/2007-June/012145.html). Consider the following class definitions: struct A { int i_; A(int i) : i_(i) {} }; struct B { A * a_; B(A * a) : a_(a) {} int a_content() { return a_ == 0 ? 0 : a_->i_; } }; B * create_B(A * a) { return new B(a); } and the corresponding boost::python glue code BOOST_PYTHON_MODULE(test_custodian_and_ward) { class_("A", no_init) .def(init()) // #1 .def("create_B", &create_B, with_custodian_and_ward_postcall<0,1, return_value_policy >()) ; class_("B1", no_init) // #2 .def(init()[with_custodian_and_ward_postcall<1,2>()]) .def("a_content", &B::a_content) ; class_("B2", no_init) // #3 .def("__init__", make_constructor(&create_B, with_custodian_and_ward_postcall<1,2>())) .def("a_content", &B::a_content) ; class_("B3", no_init) // #4 .def("__init__", make_constructor(&create_B, with_custodian_and_ward_postcall<0,1>())) .def("a_content", &B::a_content) ; } In this code #1 works as desired #2 works, but is a bit counter-intuitive because indexing suddenly starts at 1 #3 causes an "argument index out of range" error #4 runs, but fails to establish the desired custodian-and-ward relationship (i.e. B3.a_content() may crash because the containd A instance can be deleted prematurely) The pull request introduces a new policy construct_custodian_for which solves problems #2-4. It is used like this: BOOST_PYTHON_MODULE(test_custodian_and_ward) { ... class_("B1", no_init) .def(init()[construct_custodian_for<1>()]) .def("a_content", &B::a_content) ; class_("B2", no_init) .def("__init__", make_constructor(&create_B, construct_custodian_for<1>())) .def("a_content", &B::a_content) ; }

Open Graph Description: (note: I will update the documentation as well when this pull request gets accepted) This pull request proposes a fix for the long-standing problem that with_custodian_and_ward_postcall doesn't...

X Description: (note: I will update the documentation as well when this pull request gets accepted) This pull request proposes a fix for the long-standing problem that with_custodian_and_ward_postcall doesn&#...

Opengraph URL: https://github.com/boostorg/python/pull/8

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