[libsigc++2] Fix test_cpp11_lambda for gcc 4.8

[Kjell Ahlstedt <kjellahl src gnome org>]

commit cd600a31fbf8e76e25f4be4c10c0645f090a9b80
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Sat Oct 26 10:46:24 2013 +0200

    Fix test_cpp11_lambda for gcc 4.8
    
    * tests/test_cpp11_lambda.cc: Remove an unneccesary std::ref().
    Show that std::bind() can be assigned to a slot, if it's combined with
    std::function.

 tests/test_cpp11_lambda.cc |   31 ++++++++++++++++++++++++++++++-
 1 files changed, 30 insertions(+), 1 deletions(-)
---
diff --git a/tests/test_cpp11_lambda.cc b/tests/test_cpp11_lambda.cc
index 463c69e..f3d6f09 100644
--- a/tests/test_cpp11_lambda.cc
+++ b/tests/test_cpp11_lambda.cc
@@ -300,8 +300,10 @@ int main(int argc, char* argv[])
   util->check_result(result_stream, "foo(int 2, int 1) 9");
 
   //std::cout << (sigc::group(sigc::mem_fun(&bar::test), _1, _2, _3)) (sigc::ref(the_bar), 1, 2) << 
std::endl;
+  // std::ref(the_bar) is not necessary. It can make the call ambiguous.
+  // Even without std::ref() the_bar is not copied.
   result_stream << std::bind(std::mem_fn(&bar::test), std::placeholders::_1,
-    std::placeholders::_2, std::placeholders::_3)(std::ref(the_bar), 1, 2);
+    std::placeholders::_2, std::placeholders::_3)(the_bar, 1, 2);
   util->check_result(result_stream, "bar::test(int 1, int 2) 6");
 
   // same functionality as bind
@@ -317,6 +319,13 @@ int main(int argc, char* argv[])
   std::bind(sigc::ptr_fun(&foo_void), 1)();
   util->check_result(result_stream, "foo_void(int 1)");
 
+  // std::bind() does not work well together with sigc::slot and sigc::signal::connect().
+  // std::bind() typically creates a functor whose operator()() is a variadic template.
+  // SIGC_FUNCTORS_DEDUCE_RESULT_TYPE_WITH_DECLTYPE can't deduce the result type
+  // of such a functor.
+  // If the result of std::bind() is assigned to a std::function, the created
+  // functor has an unambiguous operator()().
+
   // auto-disconnect
   sigc::slot<void> sl2;
   {
@@ -337,6 +346,26 @@ int main(int argc, char* argv[])
   sl2();
   util->check_result(result_stream, "");
 
+  // More auto-disconnect
+  {
+    book guest_book("charlie");
+    //sl2 = sigc::group(&egon, sigc::ref(guest_book));
+    // sl2 = std::bind(&egon, std::ref(guest_book)); // does not compile (gcc 4.6.3)
+    std::function<void()> fn2 = std::bind(&egon, std::ref(guest_book));
+    //sl2 = fn2; // no auto-disconnect
+    sl2 = sigc::track_obj(fn2, guest_book);
+    sl2();
+    util->check_result(result_stream, "egon(string 'charlie')");
+
+    //std::cout << static_cast<std::string&>(guest_book) << std::endl;
+    result_stream << static_cast<std::string&>(guest_book);
+    util->check_result(result_stream, "egon was here");
+
+  } // auto-disconnect
+
+  sl2();
+  util->check_result(result_stream, "");
+
   // same functionality as hide
   //std::cout << (sigc::group(&foo, _1, _2)) (1,2,3) << std::endl;
   result_stream << std::bind(&foo, std::placeholders::_1, std::placeholders::_2)(1,2,3);