From 70262292733ac29e38e1041d141c72b882123f1a Mon Sep 17 00:00:00 2001
From: Jason Turner <jason@emptycrate.com>
Date: Mon, 1 Jun 2015 09:43:29 -0600
Subject: [PATCH] Apply Index expansion technique to simplify code

Thanks @sean-parent I saw the technique in your future implementation
---
 .../dispatchkit/proxy_functions_detail.hpp    | 94 ++++++++-----------
 1 file changed, 37 insertions(+), 57 deletions(-)

diff --git a/include/chaiscript/dispatchkit/proxy_functions_detail.hpp b/include/chaiscript/dispatchkit/proxy_functions_detail.hpp
index b90c8d63..a77376f4 100644
--- a/include/chaiscript/dispatchkit/proxy_functions_detail.hpp
+++ b/include/chaiscript/dispatchkit/proxy_functions_detail.hpp
@@ -53,6 +53,23 @@ namespace chaiscript
   {
     namespace detail
     {
+      template<size_t ... I>
+      struct Indexes
+      {
+      };
+
+      template<size_t S, size_t ... I> 
+      struct Make_Indexes
+      {
+        typedef typename Make_Indexes<S-1, I..., sizeof...(I)>::indexes indexes;
+      };
+
+      template<size_t ... I>
+      struct Make_Indexes<0, I...>
+      {
+        typedef Indexes<I...> indexes;
+      };
+
       /**
        * Used by Proxy_Function_Impl to return a list of all param types
        * it contains.
@@ -65,77 +82,39 @@ namespace chaiscript
         }
 
 
-      // Forward declaration
-      template<typename ... Rest> 
-        struct Try_Cast; 
-
-      template<typename Param, typename ... Rest>
-        struct Try_Cast<Param, Rest...>
-        {
-          static void do_try(const std::vector<Boxed_Value> &params, size_t generation, const Type_Conversions &t_conversions)
-          {
-            boxed_cast<Param>(params[generation], &t_conversions);
-            Try_Cast<Rest...>::do_try(params, generation+1, t_conversions);
-          }
-        };
-
-      // 0th case
-      template<>
-        struct Try_Cast<>
-        {
-          static void do_try(const std::vector<Boxed_Value> &, size_t, const Type_Conversions &)
-          {
-          }
-        };
-
-
       /**
        * Used by Proxy_Function_Impl to determine if it is equivalent to another
        * Proxy_Function_Impl object. This function is primarily used to prevent
        * registration of two functions with the exact same signatures
        */
-      template<typename Ret, typename ... Params>
-        bool compare_types_cast(Ret (*)(Params...),
+      template<typename Ret, typename ... Params, size_t ... I>
+        bool compare_types_cast(Indexes<I...>, Ret (*)(Params...),
              const std::vector<Boxed_Value> &params, const Type_Conversions &t_conversions)
-       {
+        {
           try {
-            Try_Cast<Params...>::do_try(params, 0, t_conversions);
+            std::initializer_list<void *>{(boxed_cast<Params>(params[I], &t_conversions), nullptr)...};
+            return true;
           } catch (const exception::bad_boxed_cast &) {
             return false;
           }
 
-          return true;
         }
 
-      template<typename Ret, int count, typename ... Params>
-        struct Call_Func
-        {
-
-          template<typename ... InnerParams>
-          static Ret do_call(const std::function<Ret (Params...)> &f,
-              const std::vector<Boxed_Value> &params, const Type_Conversions &t_conversions, InnerParams &&... innerparams)
-          {
-            return Call_Func<Ret, count - 1, Params...>::do_call(f, params, t_conversions, std::forward<InnerParams>(innerparams)..., params[sizeof...(Params) - count]);
-          } 
-        };
-
       template<typename Ret, typename ... Params>
-        struct Call_Func<Ret, 0, Params...>
+        bool compare_types_cast(Ret (*f)(Params...),
+             const std::vector<Boxed_Value> &params, const Type_Conversions &t_conversions)
         {
-#ifdef CHAISCRIPT_MSVC
-#pragma warning(push)
-#pragma warning(disable : 4100) /// Disable unreferenced formal parameter warning, which only shows up in MSVC I don't think there's any way around it \todo evaluate this
-#endif
-          template<typename ... InnerParams>
-            static Ret do_call(const std::function<Ret (Params...)> &f,
-                const std::vector<Boxed_Value> &, const Type_Conversions &t_conversions, InnerParams &&... innerparams)
-            {
-              return f(boxed_cast<Params>(std::forward<InnerParams>(innerparams), &t_conversions)...);
-            }
-#ifdef CHAISCRIPT_MSVC
-#pragma warning(pop)
-#endif
-        };
+          typedef typename Make_Indexes<sizeof...(Params)>::indexes indexes;
+          return compare_types_cast(indexes(), f, params, t_conversions);
+        }
+
+      template<typename Ret, typename ... Params, size_t ... I>
+        Ret call_func(Indexes<I...>, const std::function<Ret (Params...)> &f,
+            const std::vector<Boxed_Value> &params, const Type_Conversions &t_conversions)
+        {
+          return f(boxed_cast<Params>(params[I], &t_conversions)...);
+        }
+
 
       /**
        * Used by Proxy_Function_Impl to perform typesafe execution of a function.
@@ -149,7 +128,8 @@ namespace chaiscript
         {
           if (params.size() == sizeof...(Params))
           {
-            return Call_Func<Ret, sizeof...(Params), Params...>::do_call(f, params, t_conversions);
+            typedef typename Make_Indexes<sizeof...(Params)>::indexes indexes;
+            return call_func(indexes(), f, params, t_conversions);
           }
 
           throw exception::arity_error(static_cast<int>(params.size()), sizeof...(Params));