mp/function_info: Add parameter_count_v

src/common/mp/function_info.h

@@ -58,6 +58,14 @@ struct FunctionInfo<R(C::*)(Args...) const> : public FunctionInfo<R(Args...)>
     using class_type = C;
 };
 
+/**
+ * Helper template for retrieving the number of function parameters.
+ *
+ * @tparam Function       An arbitrary function type.
+ */
+template <typename Function>
+constexpr size_t parameter_count_v = FunctionInfo<Function>::args_count;
+
 /**
  * Helper template for retrieving the type of a function parameter.
  *