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Support multiple inheritance from python

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This commit allows multiple inheritance of pybind11 classes from
Python, e.g.

    class MyType(Base1, Base2):
        def __init__(self):
            Base1.__init__(self)
            Base2.__init__(self)

where Base1 and Base2 are pybind11-exported classes.

This requires collapsing the various builtin base objects
(pybind11_object_56, ...) introduced in 2.1 into a single
pybind11_object of a fixed size; this fixed size object allocates enough
space to contain either a simple object (one base class & small* holder
instance), or a pointer to a new allocation that can contain an
arbitrary number of base classes and holders, with holder size
unrestricted.

* "small" here means having a sizeof() of at most 2 pointers, which is
enough to fit unique_ptr (sizeof is 1 ptr) and shared_ptr (sizeof is 2
ptrs).

To minimize the performance impact, this repurposes
`internals::registered_types_py` to store a vector of pybind-registered
base types.  For direct-use pybind types (e.g. the `PyA` for a C++ `A`)
this is simply storing the same thing as before, but now in a vector;
for Python-side inherited types, the map lets us avoid having to do a
base class traversal as long as we've seen the class before.  The
change to vector is needed for multiple inheritance: Python types
inheriting from multiple registered bases have one entry per base.
This commit is contained in:
Jason Rhinelander
2017-02-22 21:36:09 -05:00
parent caedf74a89
commit e45c211497
11 changed files with 830 additions and 343 deletions
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14
tests/test_multiple_inheritance.cpp
View File

@@ -23,6 +23,11 @@ struct Base2 {
int i;
};
template <int N> struct BaseN {
BaseN(int i) : i(i) { }
int i;
};
struct Base12 : Base1, Base2 {
Base12(int i, int j) : Base1(i), Base2(j) { }
};
@@ -45,6 +50,15 @@ test_initializer multiple_inheritance([](py::module &m) {
py::class_<MIType, Base12>(m, "MIType")
.def(py::init<int, int>());
// Many bases for testing that multiple inheritance from many classes (i.e. requiring extra
// space for holder constructed flags) works.
#define PYBIND11_BASEN(N) py::class_<BaseN<N>>(m, "BaseN" #N).def(py::init<int>()).def("f" #N, [](BaseN<N> &b) { return b.i + N; })
PYBIND11_BASEN( 1); PYBIND11_BASEN( 2); PYBIND11_BASEN( 3); PYBIND11_BASEN( 4);
PYBIND11_BASEN( 5); PYBIND11_BASEN( 6); PYBIND11_BASEN( 7); PYBIND11_BASEN( 8);
PYBIND11_BASEN( 9); PYBIND11_BASEN(10); PYBIND11_BASEN(11); PYBIND11_BASEN(12);
PYBIND11_BASEN(13); PYBIND11_BASEN(14); PYBIND11_BASEN(15); PYBIND11_BASEN(16);
PYBIND11_BASEN(17);
// Uncommenting this should result in a compile time failure (MI can only be specified via
// template parameters because pybind has to know the types involved; see discussion in #742 for
// details).