From ceda32b912b7413b92c3c848af5a29b89f71b3b5 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 9 Feb 2022 16:33:44 +1000
Subject: [PATCH] tuple/value: fix various compile time errors

---
 tuple/value.hpp | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/tuple/value.hpp b/tuple/value.hpp
index c037158b..7211499d 100644
--- a/tuple/value.hpp
+++ b/tuple/value.hpp
@@ -250,24 +250,31 @@ namespace cruft::tuple::value {
     ///////////////////////////////////////////////////////////////////////////
     namespace detail {
         template <typename FunctionT, typename TupleT, size_t ...Index>
-        requires (
-            std::is_convertible_v<
-                std::tuple_element_t<Index, TupleT>,
-                std::common_type<
-                    std::tuple_element_t<Index, TupleT>...
-                >
-            > && ...
-        )
+        // requires (
+        //     std::is_convertible_v<
+        //         std::tuple_element_t<Index, TupleT>,
+        //         std::common_type<
+        //             std::tuple_element_t<Index, TupleT>...
+        //         >
+        //     > && ...
+        // )
         auto
-        transform_array (index::indices<Index...>, FunctionT &&func, TupleT &&val)
+        transform_array (std::index_sequence<Index...>, FunctionT &&func, TupleT &&val)
         {
-            using value_type = std::common_type<
-                std::tuple_element_t<Index, TupleT>...
+            using value_type = std::common_type_t<
+                std::invoke_result_t<
+                    FunctionT,
+                    std::tuple_element_t<Index, std::remove_cvref_t<TupleT>>
+                >...
             >;
 
-            return std::array<value_type, std::tuple_size_v<TupleT>> (
-                std::invoke (func, std::get<Index> (val))...
-            );
+            constexpr auto arity = std::tuple_size_v<
+                std::remove_cvref_t<TupleT>
+            >;
+
+            return std::array<value_type, arity> { {
+                value_type (std::invoke (func, std::get<Index> (val)))...
+            } };
         }
     }
 
@@ -281,9 +288,14 @@ namespace cruft::tuple::value {
     auto
     transform_array (FunctionT &&func, TupleT &&val)
     {
-        return transform_array (
+        return detail::transform_array (
+            std::make_index_sequence<
+                std::tuple_size_v<
+                    std::remove_cvref_t<TupleT>
+                >
+            > {},
             std::forward<FunctionT> (func),
-            std::forward<TupleT> (val)
+            std::forward<TupleT   > (val )
         );
     }
 }