Boost.Python包装原始指针但公开方法

Question

I have a class with methods that I get raw pointers to:

struct Foo {
    int getSomething() const { .. }
    void setSomethingElse(int ) { .. }
    // .. lots more getters, setters, and other methods ..
};

Foo* p = make_something();

I had originally exposed this directly to python:

py::class_<Foo, Foo*, boost::noncopyable>("Foo", py::no_init)
    .def("getSomething", &Foo::getSomething)
    // ..
;

But the Foo s I get come from an allocator that aggressively reuses memory, and my usage in python might hold onto these Foo* s longer than they actually exist as valid objects in C++. So really I want to wrap them to save off some values, eg:

struct FooWrapper {
    Foo* p;
    int val1;

    FooWrapper(Foo* p) : p(p), val1(p->getVal1()) { }

    operator Foo*() const { return p; }
    int getVal1() const { return val1; }
};

FooWrapper fw(make_something());

But now in order to use the healthy number of functions of Foo , I have to copy a whole bunch of stuff into FooWrapper . Or do I?? Is there a way to write and expose FooWrapper such that getVal1() calls fw.getVal1() but any other function calls fw.p->getSomethingElse() in a way that I can avoid copying every other method on Foo ? This is python after all, so I'm guessing there's something I can do with getattr ?

Answer 1

This was easier than I'd expected:

struct FooWrapper 
{
    // as before

    static py::object getattr(py::object self, std::string attr)
    {
        FooWrapper& fw = py::extract<FooWrapper&>(self);
        return py::getattr(py::object{py::ptr(fw.p)}, attr.c_str());
    }
};

With:

py::class_<FooWrapper, boost::noncopyable>("Foo", py::no_init)
    .def("getVal1", &FooWrapper::getVal1)
    .def("getSomethingElse", &FooWrapper::getSomethingElse)
    // ..
    // and, finally, for everything else:
    .def("__getattr__", &FooWrapper::getattr) 
;

In python then:

>>> f = get_foo() # this is really a FooWrapper
>>> f.getVal1
<bound method FooWrapper.getVal1 of <Test.FooWrapper object at 0x7faacd8d48e8>>
>>> f.getVal2
<bound method Foo.getVal2 of <Test.Foo object at 0x7faacd8d6210>>
>>> f.getVal3
AttributeError: 'Foo' object has no attribute 'getV3'