Make exception_with_errormsg take arbitrary num of params

Author: igchor

include/libpmemobj++/pexceptions.hpp

@@ -12,10 +12,13 @@
 #include <stdexcept>
 #include <string>
 #include <system_error>
+#include <tuple>
 
 #include <libpmemobj/atomic_base.h>
 #include <libpmemobj/base.h>
 
+#include <libpmemobj++/detail/integer_sequence.hpp>
+
 namespace pmem
 {
 
@@ -35,14 +38,39 @@ errormsg(void)
 #endif
 }
 
+/**
+ * Helper for exception_with_errormsg.
+ *
+ * Accepts tuple with arguments and index_sequence which correspond
+ * to all but last argument. The last element in tuple is assumed to
+ * be an error message. Before passing it to ExcT constructor it is merged
+ * with detail::errormsg()
+ */
+template <typename ExcT, size_t... I, typename Tuple>
+ExcT
+exception_with_errormsg_helper(index_sequence<I...>, Tuple &&args)
+{
+	static_assert(std::is_rvalue_reference<decltype(args)>::value,
+		      "args should be rvalue reference!");
+
+	auto msg = std::get<sizeof...(I)>(std::move(args)) + std::string(": ") +
+		detail::errormsg();
+	return ExcT(std::get<I>(std::move(args))..., std::move(msg));
+}
+
 /**
  * Generic error message decorator for pmemobj-based exceptions.
+ *
+ * It accepts arbitrary number of parameters. The last parameter must be an
+ * error message.
  */
-template <class ExcT, typename MsgT>
+template <class ExcT, typename... Args>
 ExcT
-exception_with_errormsg(const MsgT &msg)
+exception_with_errormsg(Args &&... args)
 {
-	return ExcT(msg + std::string(": ") + detail::errormsg());
+	return exception_with_errormsg_helper<ExcT>(
+		make_index_sequence<sizeof...(Args) - 1>{},
+		std::forward_as_tuple(std::forward<Args>(args)...));
 }
 } /* namespace detail */