Add utility class to easily get nth field of tuple/pair for any types

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/util.h b/lib/util.h
index 290492f..2674eaf 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -3,6 +3,7 @@
 #include <algorithm> // IWYU pragma: keep
 #include <array>
 #include <cstddef>
+#include <tuple>
 
 template<typename T, std::size_t N>
 constexpr auto
@@ -12,3 +13,23 @@ transform_array(const std::array<T, N> & in, auto && transform)
 	std::transform(in.begin(), in.end(), out.begin(), transform);
 	return out;
 }
+
+namespace {
+	template<size_t... N> struct GetNth {
+		decltype(auto)
+		operator()(const auto & tup) const
+		{
+			if constexpr (sizeof...(N) == 1) {
+				return std::get<N...>(tup);
+			}
+			else {
+				return std::tie(std::get<N>(tup)...);
+			}
+		}
+	};
+}
+
+template<size_t... N> constexpr auto Nth = GetNth<N...> {};
+constexpr auto GetFirst = Nth<0>;
+constexpr auto GetSecond = Nth<1>;
+constexpr auto GetSwapped = Nth<0, 1>;