From dfe46245d2bbf6ec70ee2a58b6ef6b94fd20f3e9 Mon Sep 17 00:00:00 2001
From: Jonathan Poelen <jo.link.noir@gmail.com>
Date: Sun, 3 Apr 2016 20:07:37 +0200
Subject: [PATCH] optimized map::at

* optimized map::at

* fixes lookup/map::at with C-style array type

* [msvc] fixes lookup

* [msvc] fixes lookup
---
 brigand/sequences/map.hpp | 135 ++++++--------------------------------
 test/map_test.cpp         |   2 +
 2 files changed, 23 insertions(+), 114 deletions(-)

diff --git a/brigand/sequences/map.hpp b/brigand/sequences/map.hpp
index a44a07c..0d1608c 100644
--- a/brigand/sequences/map.hpp
+++ b/brigand/sequences/map.hpp
@@ -13,8 +13,16 @@
 namespace brigand
 {
 
+namespace lazy
+{
+    template <typename M, typename K>
+    struct lookup
+    : decltype(M::at(type_<K>{}))
+    {};
+}
+
     template <typename M, typename K>
-    using lookup = decltype(M::at(type_<K>{}));
+    using lookup = typename lazy::lookup<M,K>::type;
 
 namespace detail
 {
@@ -47,128 +55,27 @@ namespace detail
     struct map_impl<>
     {
         template <typename U>
-        static no_such_type_ at(U);
+        static type_<no_such_type_> at(U);
 
         template <class K>
         static map_impl<K> insert(type_<K>);
     };
 
-    // fastlane for constant amortized time
-    template <class T0>
-    struct map_impl<T0> : map_inserter<T0>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-    template <class T0, class T1>
-    struct map_impl<T0, T1> : map_inserter<T0, T1>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-    template <class T0, class T1, class T2>
-    struct map_impl<T0, T1, T2> : map_inserter<T0, T1, T2>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-    template <class T0, class T1, class T2, class T3>
-    struct map_impl<T0, T1, T2, T3> : map_inserter<T0, T1, T2, T3>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-        static typename T3::second_type at(type_<typename T3::first_type>);
-
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-    template <class T0, class T1, class T2, class T3, class T4>
-    struct map_impl<T0, T1, T2, T3, T4> : map_inserter<T0, T1, T2, T3, T4>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-        static typename T3::second_type at(type_<typename T3::first_type>);
-        static typename T4::second_type at(type_<typename T4::first_type>);
-
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-    template <class T0, class T1, class T2, class T3, class T4, class T5>
-    struct map_impl<T0, T1, T2, T3, T4, T5> : map_inserter<T0, T1, T2, T3, T4, T5>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-        static typename T3::second_type at(type_<typename T3::first_type>);
-        static typename T4::second_type at(type_<typename T4::first_type>);
-        static typename T5::second_type at(type_<typename T5::first_type>);
-
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-    template <class T0, class T1, class T2, class T3, class T4, class T5, class T6>
-    struct map_impl<T0, T1, T2, T3, T4, T5, T6> : map_inserter<T0, T1, T2, T3, T4, T5, T6>
+    template <class... Ts>
+    struct map_impl : map_inserter<Ts...>
     {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-        static typename T3::second_type at(type_<typename T3::first_type>);
-        static typename T4::second_type at(type_<typename T4::first_type>);
-        static typename T5::second_type at(type_<typename T5::first_type>);
-        static typename T6::second_type at(type_<typename T6::first_type>);
+    private:
+        struct Pack : pair<typename Ts::first_type, Ts>... {};
 
-        template <typename U>
-        static no_such_type_ at(U);
-    };
+        template<class K, class P>
+        static type_<typename P::second_type> at_impl(pair<K,P>*);
 
-    template <class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7>
-    struct map_impl<T0, T1, T2, T3, T4, T5, T6, T7> : map_inserter<T0, T1, T2, T3, T4, T5, T6, T7>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-        static typename T3::second_type at(type_<typename T3::first_type>);
-        static typename T4::second_type at(type_<typename T4::first_type>);
-        static typename T5::second_type at(type_<typename T5::first_type>);
-        static typename T6::second_type at(type_<typename T6::first_type>);
-        static typename T7::second_type at(type_<typename T7::first_type>);
+    public:
+        template<class K>
+        static decltype(at_impl<K>(static_cast<Pack*>(nullptr))) at(type_<K>);
 
-        template <typename U>
-        static no_such_type_ at(U);
-    };
-
-
-    template <class T0, class T1, class T2, class T3, class T4, class T5, class T6, class T7, class... T>
-    struct map_impl<T0, T1, T2, T3, T4, T5, T6, T7, T...> : map_inserter<T0, T1, T2, T3, T4, T5, T6, T7, T...>
-    {
-        static typename T0::second_type at(type_<typename T0::first_type>);
-        static typename T1::second_type at(type_<typename T1::first_type>);
-        static typename T2::second_type at(type_<typename T2::first_type>);
-        static typename T3::second_type at(type_<typename T3::first_type>);
-        static typename T4::second_type at(type_<typename T4::first_type>);
-        static typename T5::second_type at(type_<typename T5::first_type>);
-        static typename T6::second_type at(type_<typename T6::first_type>);
-        static typename T7::second_type at(type_<typename T7::first_type>);
-
-        template <typename U>
-        static decltype(map_impl<T...>::at(U{})) at(U);
+        template<class K>
+        static type_<no_such_type_> at(K);
     };
 
     // if you have a "class already a base" error message, it means you have defined a map with the same key present more
diff --git a/test/map_test.cpp b/test/map_test.cpp
index bdcbac5..fb12119 100644
--- a/test/map_test.cpp
+++ b/test/map_test.cpp
@@ -10,6 +10,8 @@ static_assert(brigand::detail::has_at_method<brigand::map<>>::value, "at not det
 // empty maps are allowed
 static_assert(brigand::size<brigand::map<>>::value == 0, "empty map isn't empty");
 static_assert(std::is_same<brigand::lookup<brigand::map<>, int>, brigand::no_such_type_>::value, "should find no such type in empty map");
+static_assert(std::is_same<brigand::lookup<brigand::map<brigand::pair<int, int[1]>>, int>, int[1]>::value, "should be int[1]");
+static_assert(std::is_same<brigand::lookup<brigand::map<brigand::pair<int[1], int>>, int[1]>, int>::value, "should be int");
 
 using map_test = brigand::map<brigand::pair<int, bool>, brigand::pair<char, int>>;