python-nb : Add pickle.hh, implement boost archive pickling

Author: ManifoldFR

python-nb/math.cc

@@ -4,6 +4,7 @@
 
 #include "fwd.h"
 #include "serializable.hh"
+#include "pickle.hh"
 
 #include <nanobind/eigen/dense.h>
 #include <nanobind/stl/bind_vector.h>
@@ -54,6 +55,7 @@ void exposeMaths(nb::module_ &m) {
       .def(nb::self *= nb::self)
       .def(nb::self == nb::self)
       .def(nb::self != nb::self)
+      .def(python::v2::PickleVisitor<Transform3s>())
       .def(python::v2::SerializableVisitor<Transform3s>());
 
   nb::class_<Triangle>(m, "Triangle")

python-nb/pickle.hh

@@ -0,0 +1,33 @@
+#include "fwd.h"
+
+#include <boost/archive/text_oarchive.hpp>
+#include <boost/archive/text_iarchive.hpp>
+#include <sstream>
+
+#include <nanobind/stl/string.h>
+
+namespace coal::python {
+namespace v2 {
+
+/// See: https://nanobind.readthedocs.io/en/latest/classes.html#pickling
+template <typename T>
+struct PickleVisitor : nb::def_visitor<PickleVisitor<T>> {
+  template <class... Ts>
+  void execute(nb::class_<T, Ts...> &cl) {
+    using namespace nb::literals;
+    cl.def("__getstate__", [](const T &obj) -> std::string {
+        std::stringstream ss;
+        boost::archive::text_oarchive oa(ss);
+        oa & obj;
+        return ss.str();
+      }).def("__setstate__", [](T &obj, const std::string &state) {
+      // placement-new
+      std::istringstream is(state);
+      boost::archive::text_iarchive ia(is, boost::archive::no_codecvt);
+      ia >> obj;
+    });
+  }
+};
+
+}  // namespace v2
+}  // namespace coal::python