Robust type caster for STL-vector-like classes - pybind11

Question

I have a class that is quite similar to an STL-vector (the differences are not important for the pybind11 type caster, so I will ignore them here). I have written a type caster for this class. A minimal working example of my code is given below. An example showing the problem is included below the code.
The problem is that my caster is quite limited (because I have used py::array_t). In principle the interface does accept tuples, lists, and numpy-arrays. However, when I overload based on typename, the interface fails for inputted tuples and lists (simply the first overload is selected even though it is the incorrect type).
My question is: How can I make the type caster more robust? Is there an effective way to re-use as much as possible existing type casters for STL-vector-like classes?
C++ code (including pybind11 interface)
#include <iostream>
#include <vector>
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <pybind11/numpy.h>
namespace py = pybind11;
// class definition
// ----------------
template<typename T>
class Vector
{
private:
std::vector<T> mData;
public:
Vector(){};
Vector(size_t N) { mData.resize(N); };
auto data () { return mData.data (); };
auto data () const { return mData.data (); };
auto begin() { return mData.begin(); };
auto begin() const { return mData.begin(); };
auto end () { return mData.end (); };
auto end () const { return mData.end (); };
size_t size () const { return mData.size (); };
std::vector<size_t> shape() const { return std::vector<size_t>(1, mData.size()); }
std::vector<size_t> strides() const { return std::vector<size_t>(1, sizeof(T) ); }
template<typename It> static Vector<T> Copy(It first, It last) {
Vector out(last-first);
std::copy(first, last, out.begin());
return out;
}
};
// C++ functions: overload based on type
// -------------------------------------
Vector<int> foo(const Vector<int> &A){ std::cout << "int" << std::endl; return A; }
Vector<double> foo(const Vector<double> &A){ std::cout << "double" << std::endl; return A; }
// pybind11 type caster
// --------------------
namespace pybind11 {
namespace detail {
template<typename T> struct type_caster<Vector<T>>
{
public:
PYBIND11_TYPE_CASTER(Vector<T>, _("Vector<T>"));
bool load(py::handle src, bool convert)
{
if ( !convert && !py::array_t<T>::check_(src) ) return false;
auto buf = py::array_t<T, py::array::c_style | py::array::forcecast>::ensure(src);
if ( !buf ) return false;
auto rank = buf.ndim();
if ( rank != 1 ) return false;
value = Vector<T>::Copy(buf.data(), buf.data()+buf.size());
return true;
}
static py::handle cast(const Vector<T>& src, py::return_value_policy policy, py::handle parent)
{
py::array a(std::move(src.shape()), std::move(src.strides()), src.data());
return a.release();
}
};
}} // namespace pybind11::detail
// Python interface
// ----------------
PYBIND11_MODULE(example,m)
{
m.doc() = "pybind11 example plugin";
m.def("foo", py::overload_cast<const Vector<int > &>(&foo));
m.def("foo", py::overload_cast<const Vector<double> &>(&foo));
}
Example
import numpy as np
import example
print(example.foo((1,2,3)))
print(example.foo((1.5,2.5,3.5)))
print(example.foo(np.array([1,2,3])))
print(example.foo(np.array([1.5,2.5,3.5])))
Output:
int
[1 2 3]
int
[1 2 3]
int
[1 2 3]
double
[1.5 2.5 3.5]

Answer 1

A very easy solution is to specialise pybind11::detail::list_caster. The type caster now becomes as easy as
namespace pybind11 {
namespace detail {
template <typename Type> struct type_caster<Vector<Type>> : list_caster<Vector<Type>, Type> { };
}} // namespace pybind11::detail
Note that this does require Vector to have the methods:
clear()
push_back(const Type &value)
reserve(size_t n) (seems optional in testing)
Complete example
#include <iostream>
#include <vector>
#include <pybind11/pybind11.h>
#include <pybind11/stl.h>
#include <pybind11/numpy.h>
namespace py = pybind11;
// class definition
// ----------------
template<typename T>
class Vector
{
private:
std::vector<T> mData;
public:
Vector(){};
Vector(size_t N) { mData.resize(N); };
auto data () { return mData.data (); };
auto data () const { return mData.data (); };
auto begin() { return mData.begin(); };
auto begin() const { return mData.begin(); };
auto end () { return mData.end (); };
auto end () const { return mData.end (); };
size_t size () const { return mData.size (); };
void push_back(const T &value) { mData.push_back(value); }
void clear() { mData.clear(); }
void reserve(size_t n) { mData.reserve(n); }
std::vector<size_t> shape() const { return std::vector<size_t>(1, mData.size()); }
std::vector<size_t> strides() const { return std::vector<size_t>(1, sizeof(T) ); }
template<typename It> static Vector<T> Copy(It first, It last) {
printf("Vector<T>::Copy %s\n", __PRETTY_FUNCTION__);
Vector out(last-first);
std::copy(first, last, out.begin());
return out;
}
};
// C++ functions: overload based on type
// -------------------------------------
Vector<int> foo(const Vector<int> &A){ std::cout << "int" << std::endl; return A; }
Vector<double> foo(const Vector<double> &A){ std::cout << "double" << std::endl; return A; }
// pybind11 type caster
// --------------------
namespace pybind11 {
namespace detail {
template <typename Type> struct type_caster<Vector<Type>> : list_caster<Vector<Type>, Type> { };
}} // namespace pybind11::detail
// Python interface
// ----------------
PYBIND11_MODULE(example,m)
{
m.doc() = "pybind11 example plugin";
m.def("foo", py::overload_cast<const Vector<double> &>(&foo));
m.def("foo", py::overload_cast<const Vector<int > &>(&foo));
}