Converting shared_ptr<const T> fails

首先，使用 shared_ptr，通过 create_shared_ptr、accept_shared_ptr 和 register_ptr_to_python 复现所示的 C++ 绑定。跟踪针对 const 目标类型的 Boost.Python 转换路径；当 create_shared_ptr 返回的 Python Foo 能够被 accept_shared_ptr 接受且不出现 ArgumentError 时，即表示完成。

Boost Python (1.63) works well with shared_ptr<T>; if I write this in C++:

shared_ptr<Foo> create_shared_ptr() { return shared_ptr{...}; }
void accept_shared_ptr(const shared_ptr<Foo>& p) { }

...

class_<Foo, boost::noncopyable>("Foo", no_init); //Expose abstract class

register_ptr_to_python< shared_ptr<Foo> >();
def("create_shared_ptr", create_shared_ptr);
def("accept_shared_ptr", accept_shared_ptr);

Then I can write this in Python and everything works:

accept_shared_ptr(create_shared_ptr())

The problem comes when I try and wrap shared_ptr<const Foo>. (Which I need to do because I am wrapping a library that returns this.) If I modify the C++ functions as follows:

shared_ptr<const Foo> create_shared_ptr() { return shared_ptr{...}; }
void accept_shared_ptr(const shared_ptr<const Foo>& p) { }

Then I get the error:

Boost.Python.ArgumentError: Python argument types in
    w3w_python.accept_shared_ptr(Foo)
did not match C++ signature:
    accept_shared_ptr(std::shared_ptr<Foo const>)

It seems the internals are implementing conversion from python Foo to C++ shared_ptr<Foo>, but not to C++ shared_ptr<const Foo>. Using

register_ptr_to_python< shared_ptr<const Foo> >();

doesn't help. How can I fix this?