simplify enum pickle implementation, added test

Author: wjakob

include/pybind11/pybind11.h

@@ -1469,8 +1469,11 @@ struct enum_base {
         #undef PYBIND11_ENUM_OP_CONV
         #undef PYBIND11_ENUM_OP_STRICT
 
-        m_base.attr("__hash__") = cpp_function(
+        object getstate = cpp_function(
             [](object arg) { return int_(arg); }, is_method(m_base));
+
+        m_base.attr("__getstate__") = getstate;
+        m_base.attr("__hash__") = getstate;
     }
 
     PYBIND11_NOINLINE void value(char const* name_, object value, const char *doc = nullptr) {
@@ -1517,10 +1520,7 @@ template <typename Type> class enum_ : public class_<Type> {
         #if PY_MAJOR_VERSION < 3
             def("__long__", [](Type value) { return (Scalar) value; });
         #endif
-
-        // Pickling and unpickling -- needed for use with the 'multiprocessing' module
-        def(pickle([](const Type &value) { return pybind11::make_tuple((Scalar) value); },
-                   [](tuple t) { return static_cast<Type>(t[0].cast<Scalar>()); }));
+        def("__setstate__", [](Type &value, Scalar arg) { value = static_cast<Type>(arg); });
     }
 
     /// Export enumeration entries into the parent scope

tests/test_pickling.py

@@ -34,3 +34,9 @@ def test_roundtrip_with_dict(cls_name):
     assert p2.value == p.value
     assert p2.extra == p.extra
     assert p2.dynamic == p.dynamic
+
+
+def test_enum_pickle():
+    from pybind11_tests import enums as e
+    data = pickle.dumps(e.EOne, 2)
+    assert e.EOne == pickle.loads(data)