pybind/pybind11
1
0
Fork 0
mirror of https://github.com/pybind/pybind11.git synced 2026-04-19 22:39:09 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fix template trampoline overload lookup failure

Browse Source 
Problem
=======

The template trampoline pattern documented in PR #322 has a problem with
virtual method overloads in intermediate classes in the inheritance
chain between the trampoline class and the base class.

For example, consider the following inheritance structure, where `B` is
the actual class, `PyB<B>` is the trampoline class, and `PyA<B>` is an
intermediate class adding A's methods into the trampoline:

    PyB<B> -> PyA<B> -> B -> A

Suppose PyA<B> has a method `some_method()` with a PYBIND11_OVERLOAD in
it to overload the virtual `A::some_method()`.  If a Python class `C` is
defined that inherits from the pybind11-registered `B` and tries to
provide an overriding `some_method()`, the PYBIND11_OVERLOADs declared
in PyA<B> fails to find this overloaded method, and thus never invoke it
(or, if pure virtual and not overridden in PyB<B>, raises an exception).

This happens because the base (internal) `PYBIND11_OVERLOAD_INT` macro
simply calls `get_overload(this, name)`; `get_overload()` then uses the
inferred type of `this` to do a type lookup in `registered_types_cpp`.
This is where it fails: `this` will be a `PyA<B> *`, but `PyA<B>` is
neither the base type (`B`) nor the trampoline type (`PyB<B>`).  As a
result, the overload fails and we get a failed overload lookup.

The fix
=======

The fix is relatively simple: we can cast `this` passed to
`get_overload()` to a `const B *`, which lets get_overload look up the
correct class.  Since trampoline classes should be derived from `B`
classes anyway, this cast should be perfectly safe.

This does require adding the class name as an argument to the
PYBIND11_OVERLOAD_INT macro, but leaves the public macro signatures
unchanged.
This commit is contained in:
Jason Rhinelander
2016-08-29 18:16:46 -04:00
parent d9b3db3e64
commit 2097826346
3 changed files with 43 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
tests/test_virtual_functions.cpp
View File

@@ -145,6 +145,9 @@ public: \
for (unsigned i = 0; i < times; ++i) \
s += "hi"; \
return s; \
} \
std::string say_everything() { \
return say_something(1) + " " + std::to_string(unlucky_number()); \
}
A_METHODS
};
@@ -253,7 +256,8 @@ void initialize_inherited_virtuals(py::module &m) {
py::class_<A_Repeat, std::unique_ptr<A_Repeat>, PyA_Repeat>(m, "A_Repeat")
.def(py::init<>())
.def("unlucky_number", &A_Repeat::unlucky_number)
.def("say_something", &A_Repeat::say_something);
.def("say_something", &A_Repeat::say_something)
.def("say_everything", &A_Repeat::say_everything);
py::class_<B_Repeat, std::unique_ptr<B_Repeat>, PyB_Repeat>(m, "B_Repeat", py::base<A_Repeat>())
.def(py::init<>())
.def("lucky_number", &B_Repeat::lucky_number);
@@ -266,7 +270,8 @@ void initialize_inherited_virtuals(py::module &m) {
py::class_<A_Tpl, std::unique_ptr<A_Tpl>, PyA_Tpl<>>(m, "A_Tpl")
.def(py::init<>())
.def("unlucky_number", &A_Tpl::unlucky_number)
.def("say_something", &A_Tpl::say_something);
.def("say_something", &A_Tpl::say_something)
.def("say_everything", &A_Tpl::say_everything);
py::class_<B_Tpl, std::unique_ptr<B_Tpl>, PyB_Tpl<>>(m, "B_Tpl", py::base<A_Tpl>())
.def(py::init<>())
.def("lucky_number", &B_Tpl::lucky_number);