1 files changed, 68 insertions, 0 deletions
diff --git a/src/tupleref.hpp b/src/tupleref.hpp
new file mode 100644
index 0000000..c6a6dcd
--- /dev/null
+++ b/src/tupleref.hpp
@@ -0,0 +1,68 @@
+#pragma once
+
+#include <tuple>
+#include <utility>
+
+namespace phosphor
+{
+namespace dbus
+{
+namespace monitoring
+{
+
+/** @brief A tuple of references. */
+template <typename... T>
+using TupleOfRefs = std::tuple<std::reference_wrapper<T>...>;
+
+namespace detail
+{
+/** @brief Less than implementation for tuples of references. */
+template <size_t size, size_t i, typename T, typename U>
+struct TupleOfRefsLess
+{
+    static constexpr bool compare(const T& l, const U& r)
+    {
+        if (std::get<i>(l).get() < std::get<i>(r).get())
+        {
+            return true;
+        }
+        if (std::get<i>(r).get() < std::get<i>(l).get())
+        {
+            return false;
+        }
+        return TupleOfRefsLess < size, i + 1, T, U >::compare(l, r);
+    }
+};
+
+/** @brief Less than specialization for tuple element sizeof...(tuple) +1. */
+template <size_t size, typename T, typename U>
+struct TupleOfRefsLess<size, size, T, U>
+{
+    static constexpr bool compare(const T& l, const U& r)
+    {
+        return false;
+    }
+};
+} // namespace detail
+
+/** @brief Less than comparison for tuples of references. */
+struct TupleOfRefsLess
+{
+    template <typename... T, typename... U>
+    constexpr bool operator()(
+        const TupleOfRefs<T...>& l,
+        const TupleOfRefs<U...>& r) const
+    {
+        static_assert(sizeof...(T) == sizeof...(U),
+                      "Cannot compare tuples of different lengths.");
+        return detail::TupleOfRefsLess <
+               sizeof...(T),
+               0,
+               TupleOfRefs<T...>,
+               TupleOfRefs<U... >>::compare(l, r);
+    }
+};
+
+} // namespace monitoring
+} // namespace dbus
+} // namespace phosphor