wip: Try to add arithmetic type support

Author: jorisv

include/eigenpy/variant.hpp

@@ -12,6 +12,8 @@
 #include <boost/mpl/for_each.hpp>
 #include <boost/mpl/vector.hpp>
 
+#include <type_traits>
+
 #ifdef EIGENPY_WITH_CXX17_SUPPORT
 #include <variant>
 #endif
@@ -96,6 +98,7 @@ struct VariantValueToObject : VariantVisitorType<PyObject*, Variant> {
   using Base::operator();
 };
 
+
 /// Convert {boost,std}::variant<class...> alternative reference to a Python
 /// object. This converter return the alternative reference. The code that
 /// create the reference holder is taken from \see
@@ -110,7 +113,20 @@ struct VariantRefToObject : VariantVisitorType<PyObject*, Variant> {
     return Base::visit(VariantRefToObject(), v);
   }
 
-  template <typename T>
+  template <typename T,
+            typename std::enable_if<
+                std::is_arithmetic<typename std::remove_cv<
+                    typename std::remove_reference<T>::type>::type>::value,
+                bool>::type = true>
+  result_type operator()(T t) const {
+    return boost::python::incref(boost::python::object(t).ptr());
+  }
+
+  template <typename T,
+            typename std::enable_if<
+                !std::is_arithmetic<typename std::remove_cv<
+                    typename std::remove_reference<T>::type>::type>::value,
+                bool>::type = true>
   result_type operator()(T& t) const {
     return boost::python::detail::make_reference_holder::execute(&t);
   }
@@ -198,6 +214,7 @@ struct VariantConverter {
   static void registration() {
     typedef details::VariantValueToObject<variant_type> variant_to_value;
     typedef typename details::VariantAlternatives<variant_type>::types types;
+
     boost::python::to_python_converter<variant_type, variant_to_value>();
     boost::mpl::for_each<types>(
         details::VariantImplicitlyConvertible<variant_type>());

unittest/python/test_variant.py.in

@@ -5,8 +5,10 @@ V1 = variant_module.V1
 V2 = variant_module.V2
 VariantHolder = variant_module.VariantHolder
 VariantNoneHolder = variant_module.VariantNoneHolder
+VariantArithmeticHolder = variant_module.VariantArithmeticHolder
 make_variant = variant_module.make_variant
 make_variant_none = variant_module.make_variant_none
+make_variant_arithmetic = variant_module.make_variant_arithmetic
 
 variant = make_variant()
 assert isinstance(variant, V1)
@@ -46,10 +48,6 @@ assert variant_holder.variant.v == v2.v
 # Test variant that hold a None value
 v_none = make_variant_none()
 assert v_none is None
-v_none = 1
-assert v_none == 1
-v_none = None
-assert v_none is None
 
 variant_none_holder = VariantNoneHolder()
 v_none = variant_none_holder.variant
@@ -62,3 +60,19 @@ assert variant_none_holder.variant.v == 1
 v1 = variant_none_holder.variant
 v1.v = 10
 assert variant_none_holder.variant.v == 10
+# variant_none_holder.variant = None
+
+
+# Test variant that hold base type
+v_arithmetic = make_variant_arithmetic()
+assert isinstance(v_arithmetic, int)
+
+variant_arithemtic_holder = VariantArithmeticHolder()
+assert isinstance(variant_arithemtic_holder.variant, int)
+variant_arithemtic_holder.variant = 2.0
+assert variant_arithemtic_holder.variant == 2
+assert isinstance(variant_arithemtic_holder.variant, float)
+# Arithmetic type doesn't support reference
+v1 = variant_arithemtic_holder.variant
+v1 = 3
+assert variant_arithemtic_holder.variant != v1

unittest/variant.cpp.in

@@ -34,10 +34,14 @@ struct MyVariantNoneHelper<std::variant<Alternatives...> > {
 
 typedef typename MyVariantNoneHelper<VARIANT<V1> >::type MyVariantNone;
 
+typedef VARIANT<int, double> MyVariantArithmetic;
+
 MyVariant make_variant() { return V1(); }
 
 MyVariantNone make_variant_none() { return MyVariantNone(); }
 
+MyVariantArithmetic make_variant_arithmetic() { return MyVariantArithmetic(); }
+
 struct VariantHolder {
   MyVariant variant;
 };
@@ -46,6 +50,10 @@ struct VariantNoneHolder {
   MyVariantNone variant;
 };
 
+struct VariantArithmeticHolder {
+  MyVariantArithmetic variant;
+};
+
 BOOST_PYTHON_MODULE(@MODNAME@) {
   using namespace eigenpy;
 
@@ -74,4 +82,16 @@ BOOST_PYTHON_MODULE(@MODNAME@) {
                     bp::make_getter(&VariantNoneHolder::variant,
                                     ConverterNone::return_internal_reference()),
                     bp::make_setter(&VariantNoneHolder::variant));
+
+  typedef eigenpy::VariantConverter<MyVariantArithmetic> ConverterArithmetic;
+  ConverterArithmetic::registration();
+  bp::def("make_variant_arithmetic", make_variant_arithmetic);
+
+  boost::python::class_<VariantArithmeticHolder>("VariantArithmeticHolder",
+                                                 bp::init<>())
+      .add_property(
+          "variant",
+          bp::make_getter(&VariantArithmeticHolder::variant,
+                          ConverterArithmetic::return_internal_reference()),
+          bp::make_setter(&VariantArithmeticHolder::variant));
 }