From 76b1efe12e6f842a9244ff8309963a4f82f87de6 Mon Sep 17 00:00:00 2001
From: Rapptz <rapptz@gmail.com>
Date: Sat, 31 May 2014 22:04:10 -0400
Subject: [PATCH] Revamp EnableIf and DisableIf to use a much better variadic
 condition checking

---
 sol/proxy.hpp  | 12 ++++++------
 sol/traits.hpp | 26 +++++++++++++++++++-------
 2 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/sol/proxy.hpp b/sol/proxy.hpp
index 8dc20d13..b30e558d 100644
--- a/sol/proxy.hpp
+++ b/sol/proxy.hpp
@@ -57,13 +57,13 @@ public:
         return *this;
     }
 
-    template<typename U>
-    EnableIf<Function<Unqualified<U>>> operator=(U&& other) {
+    template<typename U, EnableIf<Function<Unqualified<U>>> = 0>
+    void operator=(U&& other) {
         tbl.set_function(key, std::forward<U>(other));
     }
 
-    template<typename U>
-    DisableIf<Function<Unqualified<U>>> operator=(U&& other) {
+    template<typename U, DisableIf<Function<Unqualified<U>>> = 0>
+    void operator=(U&& other) {
         tbl.set(key, std::forward<U>(other));
     }
 
@@ -129,6 +129,6 @@ inline bool operator!= (const proxy<Table, Key>& right, T&& left) {
     return right.template get<Decay<T>>() != left;
 }
 
-} // sol
-
+} // sol
+
 #endif // SOL_PROXY_HPP
diff --git a/sol/traits.hpp b/sol/traits.hpp
index daddd3f8..f4bbc29a 100644
--- a/sol/traits.hpp
+++ b/sol/traits.hpp
@@ -32,11 +32,26 @@ struct are_same : std::true_type { };
 template<class T, class U, class... Args>
 struct are_same<T, U, Args...> : std::integral_constant <bool, std::is_same<T, U>::value && are_same<T, Args...>::value> { };
 
-template<typename T, typename R = void>
-using EnableIf = typename std::enable_if<T::value, R>::type;
+template<bool B>
+using Bool = std::integral_constant<bool, B>;
 
-template<typename T, typename R = void>
-using DisableIf = typename std::enable_if<!T::value, R>::type;
+template<typename T>
+using Not = Bool<!T::value>;
+
+template<typename Condition, typename Then, typename Else>
+using If = typename std::conditional<Condition::value, Then, Else>::type;
+
+template<typename... Args>
+struct And : Bool<true> {};
+
+template<typename T, typename... Args>
+struct And<T, Args...> : If<T, And<Args...>, Bool<false>> {};
+
+template<typename... Args>
+using EnableIf = typename std::enable_if<And<Args...>::value, int>::type;
+
+template<typename... Args>
+using DisableIf = typename std::enable_if<Not<And<Args...>>::value, int>::type;
 
 template<typename T>
 using Unqualified = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
@@ -70,9 +85,6 @@ struct is_specialization_of : std::false_type { };
 template <typename... T, template <typename...> class Templ>
 struct is_specialization_of<Templ<T...>, Templ> : std::true_type { };
 
-template<bool B>
-using Bool = std::integral_constant<bool, B>;
-
 namespace detail {
 template<typename T, bool isclass = std::is_class<Unqualified<T>>::value>
 struct is_function_impl : std::is_function<typename std::remove_pointer<T>::type> {};