Export through structures

[leoll2]

Hello!
I'm having troubles to export data structures that contain eigen members.

Example
This is a minimal example of what I would be able to do, but doesn't work.
Suppose that I have a struct like this:

struct Foo {
    int a;
    Eigen::Vector3d b;
};

I export it:

BOOST_PYTHON_MODULE(libhello) {
  SetupEigenConverters();

  class_<Foo>("Foo", init<>())
    .def_readonly("a", &Foo::a)
    .def_readonly("b", &Foo::b)
  ;
}

Then I try to work with it in Python:

import libhello
foo = libhello.Foo()
print(foo.b)

Unfortunately, I get an error like this:

TypeError: No Python class registered for C++ class Eigen::Matrix<double, 3, 1, 0, 3, 1>

Another example
This example works, but it is not exactly what I want.

struct Foo {
    int a;
    Eigen::Vector3e b;
    Eigen::Vector3d getB(void) { return b; }
};

class_<Foo>("Foo", init<>())
    .def_readonly("a", &Foo::a)
    .add_property("b", &Foo::getB)    // <- note the explicit getter
  ;

What is the issue?
These are just minimal examples, but in a real use case I have a complex hierarchy of classes. If I were to define an explicit getter for each attribute, then the complexity would easily explode. I don't really understand why I get the above error, the class should be already defined, no? If not, then why do the methods that directly return an eigen type work?

[mhkabir]

Hey @jslee02, any help on this would be greatly appreciated!