Merge pull request #2254 from adriendelsalle/fix-reducer-optional-assignment

Fix reducers assignment

Author: JohanMabille

docs/source/compilers.rst

@@ -70,7 +70,13 @@ Workarounds for this compiler bug arise in various files of the code base.
 Everywhere, the handling of `Clang < 3.8` is wrapped with checks for the
 ``X_OLD_CLANG`` macro.
 
-The support of `Clang < 4.0` is dropped in xtensor 0.22.
+**The support of `Clang < 4.0` is dropped in xtensor 0.22.**
+
+Clang-cl and ``std::get``
+-------------------------
+
+`Clang-cl` does not allow to call ``std::get`` with ``*this`` as parameter from a class inheriting from std::tuple.
+In that case, we explicitly upcast to ``std::tuple``.
 
 GCC < 5.1 and ``std::is_trivially_default_constructible``
 ---------------------------------------------------------

include/xtensor/xaccumulator.hpp

@@ -25,18 +25,27 @@ namespace xt
 
 #define DEFAULT_STRATEGY_ACCUMULATORS evaluation_strategy::immediate_type
 
+    namespace detail
+    {
+        template <class V = void>
+        struct accumulator_identity: xtl::identity
+        {
+            using value_type = V;
+        };
+    }
     /**************
      * accumulate *
      **************/
 
-    template <class ACCUMULATE_FUNC, class INIT_FUNC = xtl::identity>
+    template <class ACCUMULATE_FUNC, class INIT_FUNC = detail::accumulator_identity<void>>
     struct xaccumulator_functor
         : public std::tuple<ACCUMULATE_FUNC, INIT_FUNC>
     {
         using self_type = xaccumulator_functor<ACCUMULATE_FUNC, INIT_FUNC>;
         using base_type = std::tuple<ACCUMULATE_FUNC, INIT_FUNC>;
         using accumulate_functor_type = ACCUMULATE_FUNC;
         using init_functor_type = INIT_FUNC;
+        using init_value_type = typename init_functor_type::value_type;
 
         xaccumulator_functor()
             : base_type()
@@ -188,9 +197,10 @@ namespace xt
         template <class F, class E>
         inline auto accumulator_impl(F&& f, E&& e, std::size_t axis, evaluation_strategy::immediate_type)
         {
-            using accumulate_functor = std::decay_t<decltype(xt::get<0>(f))>;
-            using function_return_type = typename accumulate_functor::result_type;
-            using result_type = xaccumulator_return_type_t<std::decay_t<E>, function_return_type>;
+            using init_type = typename F::init_value_type;
+            using init_functor_type = typename F::init_functor_type;
+            using return_type = std::conditional_t<std::is_same<init_type, void>::value, typename std::decay_t<E>::value_type, init_type>;
+            using result_type = xaccumulator_return_type_t<std::decay_t<E>, return_type>;
 
             if (axis >= e.dimension())
             {
@@ -232,7 +242,8 @@ namespace xt
                 inner_loop_size = inner_loop_size - inner_stride;
 
                 // activate the init loop if we have an init function other than identity
-                if (!std::is_same<std::decay_t<decltype(xt::get<1>(f))>, xtl::identity>::value)
+                if (!std::is_same<std::decay_t<typename F::init_functor_type>, 
+                                  typename detail::accumulator_identity<init_type>>::value)
                 {
                     accumulator_init_with_f(xt::get<1>(f), result, axis);
                 }
@@ -255,10 +266,10 @@ namespace xt
         template <class F, class E>
         inline auto accumulator_impl(F&& f, E&& e, evaluation_strategy::immediate_type)
         {
-            using accumulate_functor = std::decay_t<decltype(xt::get<0>(f))>;
-            using T = typename accumulate_functor::result_type;
+            using init_type = typename F::init_value_type;
+            using return_type = std::conditional_t<std::is_same<init_type, void>::value, typename std::decay_t<E>::value_type, init_type>;
+            using result_type = xaccumulator_return_type_t<std::decay_t<E>, return_type>;
 
-            using result_type = xaccumulator_linear_return_type_t<std::decay_t<E>, T>;
             std::size_t sz = e.size();
             auto result = result_type::from_shape({sz});
 

include/xtensor/xassign.hpp

@@ -342,7 +342,8 @@ namespace xt
         template <class T>
         static constexpr bool simd_size_impl() { return xt_simd::simd_traits<T>::size > 1 || (is_bool<T>::value && use_xsimd()); }
         static constexpr bool simd_size() { return simd_size_impl<e1_value_type>() && simd_size_impl<e2_value_type>(); }
-        static constexpr bool simd_interface() { return has_simd_interface<E2, requested_value_type>(); }
+        static constexpr bool simd_interface() { return has_simd_interface<E1, requested_value_type>() && 
+                                                        has_simd_interface<E2, requested_value_type>(); }
 
     public: