Explicitly casting ratio to target type on unit cast

bernedom · Nov 23, 2022 · ea979be · ea979be
1 parent fadcffb
commit ea979be
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Showing 2 changed files with 12 additions and 1 deletion.
diff --git a/include/SI/detail/unit_cast.h b/include/SI/detail/unit_cast.h
@@ -13,6 +13,7 @@
 
 #include "detail.h"
 #include <ratio>
+#include <type_traits>
 
 namespace SI::detail {
 
@@ -28,11 +29,20 @@ constexpr auto unit_cast(const _rhs_T &rhs) {
                      typename _rhs_T::internal_type, typename _rhs_T::ratio>,
               _rhs_T>::value,
       "is of type unit_t or a derived class");
+
   using conversion_ratio =
       std::ratio_divide<typename _rhs_T::ratio, typename _target_type::ratio>;
+  static_assert(std::is_convertible<decltype(conversion_ratio::den),
+                                    typename _rhs_T::internal_type>::value,
+                "conversion ratio denominator is convertible to internal type");
 
+  // the static cast is needed because MSVC will print a warning without it
+  // because of a possible loss of precision when rhs is of type double
   return _target_type(
-      ((rhs.value() * conversion_ratio::num) / conversion_ratio::den));
+      ((rhs.value() * static_cast<typename _target_type::internal_type>(
+                          conversion_ratio::num)) /
+       static_cast<typename _target_type::internal_type>(
+           conversion_ratio::den)));
 }
 
 template <typename _unit_lhs, typename _unit_rhs>

diff --git a/test/src/detail_tests/unit_t_conversions_tests.cc b/test/src/detail_tests/unit_t_conversions_tests.cc
@@ -4,6 +4,7 @@
 #include <SI/detail/unit.h>
 
 #include <cstdint>
+#include <iostream>
 #include <type_traits>
 
 using namespace SI::detail;