meta: add index sequence with types as indices

1 files changed, 20 insertions, 2 deletions

diff --git a/compat/meta.hpp b/compat/meta.hpp
index b1c1dd1a..900c515f 100644
--- a/compat/meta.hpp
+++ b/compat/meta.hpp
@@ -1,6 +1,8 @@
 #pragma once
 
+#include <type_traits>
 #include <tuple>
+#include <cstddef>
 
 namespace meta {
 
@@ -29,7 +31,20 @@ namespace detail {
     {
         using type = inst<xs...>;
     };
-}
+
+    template<typename N, N max, N pos, typename... xs>
+    struct index_sequence_
+    {
+        using part = std::integral_constant<N, pos>;
+        using type = typename index_sequence_<N, max, pos+1, xs..., part>::type;
+    };
+
+    template<typename N, N max, typename... xs>
+    struct index_sequence_<N, max, max, xs...>
+    {
+        using type = std::tuple<xs...>;
+    };
+} // ns detail
 
 
 template<typename... xs>
@@ -50,4 +65,7 @@ using butlast = reverse<rest<reverse<xs...>>>;
 template<typename... xs>
 using last = lift<first, reverse<xs...>>;
 
-}
+template<std::size_t max>
+using index_sequence = typename detail::index_sequence_<std::size_t, max, std::size_t(0)>::type;
+
+} // ns meta