More specific templates

Author: WardBrian

stan/math/prim/meta/forward_as.hpp

@@ -54,13 +54,12 @@ inline T_actual&& forward_as(T_actual&& a) {  // NOLINT
  * @return nothing, this always throws
  * @throw always throws std::runtime_error
  */
-template <
-    typename T_desired, typename T_actual,
-    require_any_not_eigen_t<T_desired, T_actual>* = nullptr,
-    typename = std::enable_if_t<
-        !std::is_same<std::decay<T_actual>, std::decay<T_desired>>::value
-        && !(std::is_arithmetic_v<std::decay_t<
-                 T_desired>> && std::is_arithmetic_v<std::decay_t<T_actual>>)>>
+template <typename T_desired, typename T_actual,
+          require_any_not_eigen_t<T_desired, T_actual>* = nullptr,
+          typename = std::enable_if_t<
+              !std::is_same<std::decay<T_actual>, std::decay<T_desired>>::value
+              && !(std::is_floating_point_v<std::decay_t<T_desired>>
+                   && std::is_integral_v<std::decay_t<T_actual>>)>>
 inline T_desired forward_as(const T_actual& a) {
   throw std::runtime_error("Wrong type assumed! Please file a bug report.");
 }
@@ -80,13 +79,10 @@ inline T_desired forward_as(const T_actual& a) {
  * @param a input value
  * @return a
  */
-template <
-    typename T_desired, typename T_actual,
-    typename = std::enable_if_t<
-        !std::is_same_v<
-            std::decay_t<T_actual>,
-            std::decay_t<
-                T_desired>> && std::is_arithmetic_v<std::decay_t<T_desired>> && std::is_arithmetic_v<std::decay_t<T_actual>>>>
+template <typename T_desired, typename T_actual,
+          typename
+          = std::enable_if_t<std::is_floating_point_v<std::decay_t<T_desired>>
+                             && std::is_integral_v<std::decay_t<T_actual>>>>
 inline T_desired forward_as(const T_actual& a) {
   return static_cast<T_desired>(a);
 }