From 6b7dc4be36b8797d50698128344e62535fc61304 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vin=C3=ADcius=20dos=20Santos=20Oliveira?=
 <vini.ipsmaker@gmail.com>
Date: Wed, 21 May 2014 17:37:16 -0300
Subject: [PATCH] Greatly improved concepts/traits definition.

The improvement was based on feedback[1] from "Felipe Magno de Almeida"
<felipe.m.almeida@gmail.com>.

[1] http://pastie.org/9196937
---
 include/boost/http/traits.hpp | 64 +++++++----------------------------
 src/tests/socket_concept.cpp  | 29 ++++++++++++----
 2 files changed, 35 insertions(+), 58 deletions(-)

diff --git a/include/boost/http/traits.hpp b/include/boost/http/traits.hpp
index ed481f8..231440f 100644
--- a/include/boost/http/traits.hpp
+++ b/include/boost/http/traits.hpp
@@ -13,69 +13,31 @@ struct is_message: public std::true_type {}; //< TODO: refine concept
 
 namespace detail {
 
-template<class T, bool>
-struct has_outgoing_state_helper
-{
-    static constexpr bool value = false;
-};
-
-template<class T>
-struct has_outgoing_state_helper<T, true>
-{
-    static constexpr bool f(...) {return false;}
-
-    static constexpr bool f(decltype((static_cast<T const*>(0))->outgoing_state())*)
-    {
-        return std::is_same<decltype((static_cast<T*>(0))->outgoing_state()),
-                            boost::http::outgoing_state>::value;
-    }
-
-    static constexpr bool value = f(0);
-};
+template <typename T, typename Enable = std::true_type>
+struct has_outgoing_state : std::false_type
+{};
 
-template<class T, bool = is_class<T>::value /* TODO: make it work on is_final<T>::value */>
+template <typename T>
 struct has_outgoing_state
-{
-    static bool constexpr value = false;
-};
-
-template<class T>
-struct has_outgoing_state<T, true>
-{
-    struct Fallback {
-        int outgoing_state;
-    };
- 
-    struct Derived : T, Fallback { };
- 
-    template<typename C, C>
-    struct ChT;
- 
-    template<typename C>
-    static std::false_type f(ChT<int Fallback::*, &C::outgoing_state>*);
-
-    template<typename C>
-    static std::true_type f(...);
-
-    static bool constexpr value2 = decltype(f<Derived>(0))::value;
-
-    static bool constexpr value = value2 && has_outgoing_state_helper<T, value2>::value;
-};
+<T, typename std::is_convertible<decltype(static_cast<T const*>(nullptr)
+                                          ->outgoing_state()),
+                                 boost::http::outgoing_state>::type>
+  : std::true_type
+{};
 
 template<class T>
-bool constexpr is_http_socket_helper()
+constexpr bool is_http_socket_helper()
 {
-    return is_message<T>::value
-        && has_outgoing_state<T>::value;
+    return is_message<T>::value && has_outgoing_state<T>::value;
 }
 
 } // namespace detail
 
 template<class T>
 struct is_socket
-    : public std::conditional<detail::is_http_socket_helper<T>(),
-                              std::true_type, std::false_type>::type
+    : std::integral_constant<bool, detail::is_http_socket_helper<T>()>
 {};
 
 } // namespace http
 } // namespace boost
+
diff --git a/src/tests/socket_concept.cpp b/src/tests/socket_concept.cpp
index dd71e4d..d538ba9 100644
--- a/src/tests/socket_concept.cpp
+++ b/src/tests/socket_concept.cpp
@@ -5,31 +5,46 @@
 #include <boost/http/traits.hpp>
 
 class A
-{
-};
+{};
 
-class B
+struct B
 {
-public:
     boost::http::outgoing_state outgoing_state() const;
 };
 
-class C: public B
+struct C: B
 {
 };
 
-class D
+struct D
 {
-public:
     int outgoing_state() const;
 };
 
+struct E
+{
+    boost::http::outgoing_state outgoing_state();
+};
+
+struct F
+{
+    struct X
+    {
+        operator boost::http::outgoing_state();
+    };
+
+    X outgoing_state() const;
+};
+
 BOOST_AUTO_TEST_CASE(Simple_attributes) {
     using namespace boost::http;
 
     BOOST_CHECK(!is_socket<int>::value);
     BOOST_CHECK(!is_socket<A>::value);
+    BOOST_CHECK(is_socket<B>::value);
     BOOST_CHECK(is_socket<C>::value);
     BOOST_CHECK(!is_socket<D>::value);
+    BOOST_CHECK(!is_socket<E>::value);
+    BOOST_CHECK(is_socket<F>::value);
     BOOST_CHECK(is_socket<basic_socket<embedded_server>>::value);
 }