[libsigc++2/variadic_mem_fun2] Add member_method_class<>::type type trait.

[Murray Cumming <murrayc src gnome org>]

commit 83c6b74ca7ff669a522f0796d69e8b3f8f5ad515
Author: Murray Cumming <murrayc murrayc com>
Date:   Sat Mar 5 23:46:57 2016 +0100

    Add member_method_class<>::type type trait.

 sigc++/member_method_trait.h      |   29 +++++++++++++++++++++++++++++
 tests/test_member_method_trait.cc |   25 +++++++++++++++++++++++--
 2 files changed, 52 insertions(+), 2 deletions(-)
---
diff --git a/sigc++/member_method_trait.h b/sigc++/member_method_trait.h
index 7517ab4..a7ea0e2 100644
--- a/sigc++/member_method_trait.h
+++ b/sigc++/member_method_trait.h
@@ -80,7 +80,36 @@ struct member_method_is_volatile<T_result (T_obj::*)(T_arg...) const volatile>
 };
 
 
+//member method class:
 
+template <class T_result, class... T_arg>
+struct member_method_class
+{
+};
+
+template <class T_obj, class T_result, class... T_arg>
+struct member_method_class<T_result(T_obj::*)(T_arg...)>
+{
+  using type = T_obj;
+};
+
+template <class T_obj, class T_result, class... T_arg>
+struct member_method_class<T_result(T_obj::*)(T_arg...) volatile>
+{
+  using type = T_obj;
+};
+
+template <class T_obj, class T_result, class... T_arg>
+struct member_method_class<T_result(T_obj::*)(T_arg...) const>
+{
+  using type = T_obj;
+};
+
+template <class T_obj, class T_result, class... T_arg>
+struct member_method_class<T_result(T_obj::*)(T_arg...) const volatile>
+{
+  using type = T_obj;
+};
 
 } /* namespace sigc */
 
diff --git a/tests/test_member_method_trait.cc b/tests/test_member_method_trait.cc
index 8f7d2d6..e8d702a 100644
--- a/tests/test_member_method_trait.cc
+++ b/tests/test_member_method_trait.cc
@@ -4,6 +4,7 @@
 
 #include <cstdlib>
 #include <sigc++/member_method_trait.h>
+#include <type_traits>
 
 namespace
 {
@@ -19,7 +20,7 @@ public:
 
 } // end anonymous namespace
 
-int main()
+void test_member_method_is_const()
 {
   static_assert(!sigc::member_method_is_const<decltype(&Something::some_func)>::value,
     "member_method_is_const failed to identify a non-const member method.");
@@ -32,18 +33,38 @@ int main()
 
   static_assert(sigc::member_method_is_const<decltype(&Something::some_const_volatile_func)>::value,
     "member_method_is_const failed to identify a const member method.");
+}
 
-
+void test_member_method_is_volatile()
+{
   static_assert(!sigc::member_method_is_volatile<decltype(&Something::some_func)>::value,
     "member_method_is_const failed to identify a non-volatile member method.");
 
+  static_assert(!sigc::member_method_is_volatile<decltype(&Something::some_const_func)>::value,
+    "member_method_is_const failed to identify a non-volatile member method.");
+
   static_assert(sigc::member_method_is_volatile<decltype(&Something::some_volatile_func)>::value,
     "member_method_is_const failed to identify a volatile member method.");
 
   static_assert(sigc::member_method_is_volatile<decltype(&Something::some_const_volatile_func)>::value,
     "member_method_is_const failed to identify a volatile member method.");
+}
 
+void test_member_method_class_type()
+{
+  static_assert(std::is_same<
+    sigc::member_method_class<decltype(&Something::some_func)>::type,
+    Something>::value,
+    "member_method_class_type failed to identify the class type.");
+}
+
+
+int main()
+{
+  test_member_method_is_const();
+  test_member_method_is_volatile();
 
+  test_member_method_class_type();
 
   return EXIT_SUCCESS;
 }