Merge pull request #730 from Radnyx/fix/msvc-empty-bases

build: MSVC workaround for empty base classes

Author: mpusz

src/core/include/mp-units/bits/hacks.h

@@ -146,6 +146,16 @@ MP_UNITS_DIAGNOSTIC_POP
 
 #endif
 
+#if MP_UNITS_COMP_MSVC
+
+#define MP_UNITS_EMPTY_BASES_WORKAROUND __declspec(empty_bases)
+
+#else
+
+#define MP_UNITS_EMPTY_BASES_WORKAROUND
+
+#endif
+
 #if !defined MP_UNITS_API_NO_CRTP && __cpp_explicit_this_parameter
 
 #define MP_UNITS_API_NO_CRTP 1

src/core/include/mp-units/framework/unit.h

@@ -226,7 +226,7 @@ struct propagate_point_origin<U, true> {
 };
 
 template<UnitMagnitude auto M, Unit U>
-struct scaled_unit_impl : detail::unit_interface, detail::propagate_point_origin<U> {
+struct MP_UNITS_EMPTY_BASES_WORKAROUND scaled_unit_impl : detail::unit_interface, detail::propagate_point_origin<U> {
   using _base_type_ = scaled_unit_impl;  // exposition only
   static constexpr UnitMagnitude auto _mag_ = M;
   static constexpr U _reference_unit_{};
@@ -461,7 +461,9 @@ struct common_unit final : decltype(detail::get_common_scaled_unit(U1{}, U2{}, R
 namespace detail {
 
 template<typename... Expr>
-struct derived_unit_impl : detail::unit_interface, detail::expr_fractions<one, Expr...> {
+struct MP_UNITS_EMPTY_BASES_WORKAROUND derived_unit_impl :
+    detail::unit_interface,
+    detail::expr_fractions<one, Expr...> {
   using _base_type_ = derived_unit_impl;  // exposition only
 };