[glibmm] Revert "Avoid compiler warnings from function pointer conversions"

[Kjell Ahlstedt <kjellahl src gnome org>]

commit d3ca7e5e260dcf96fe3da8a04fadcd0e4e944971
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Jul 17 11:55:14 2018 +0200

    Revert "Avoid compiler warnings from function pointer conversions"
    
    This reverts commit fa85bd1161d5d914095d1a3f9b620da294c9af79.
    
    This can be done in a better way by keeping the union in a template function.

 gio/giomm/socketsource.cc         | 26 ++++----------------------
 glib/glibmm/main.cc               | 26 +++++---------------------
 tests/giomm_stream_vfuncs/main.cc |  2 +-
 tests/glibmm_vector/main.cc       | 13 ++-----------
 4 files changed, 12 insertions(+), 55 deletions(-)
---
diff --git a/gio/giomm/socketsource.cc b/gio/giomm/socketsource.cc
index 24248c85..76249134 100644
--- a/gio/giomm/socketsource.cc
+++ b/gio/giomm/socketsource.cc
@@ -54,19 +54,6 @@ giomm_socketsource_callback(GSocket*, GIOCondition condition, void* user_data)
   return giomm_generic_socket_callback(slot, condition);
 }
 
-GSourceFunc giomm_socketsource_cb_as_gsourcefunc()
-{
-  // Conversion between different types of function pointers with
-  // reinterpret_cast can make gcc8 print a warning.
-  // https://github.com/libsigcplusplus/libsigcplusplus/issues/1
-  union {
-    GSourceFunc ps;
-    decltype(&giomm_socketsource_callback) pss;
-  } u;
-  u.pss = &giomm_socketsource_callback;
-  return u.ps;
-}
-
 } // anonymous namespace
 
 namespace Gio
@@ -85,13 +72,8 @@ SignalSocket::connect(const sigc::slot<bool(Glib::IOCondition)>& slot,
 {
   GSource* const source =
     g_socket_create_source(socket->gobj(), (GIOCondition)condition, Glib::unwrap(cancellable));
-
-  union {
-    GSourceFunc ps;
-    decltype(&giomm_signalsocket_callback) pss;
-  } u;
-  u.pss = &giomm_signalsocket_callback;
-  return Glib::Source::attach_signal_source(slot, priority, source, context_, u.ps);
+  return Glib::Source::attach_signal_source(
+    slot, priority, source, context_, (GSourceFunc)&giomm_signalsocket_callback);
 }
 
 SignalSocket
@@ -122,7 +104,7 @@ SocketSource::SocketSource(const Glib::RefPtr<Socket>& socket, Glib::IOCondition
   const Glib::RefPtr<Cancellable>& cancellable)
 : IOSource(
     g_socket_create_source(socket->gobj(), (GIOCondition)condition, Glib::unwrap(cancellable)),
-    giomm_socketsource_cb_as_gsourcefunc())
+    (GSourceFunc)&giomm_socketsource_callback)
 {
 }
 
@@ -130,7 +112,7 @@ SocketSource::SocketSource(GSocket* socket, Glib::IOCondition condition,
   const Glib::RefPtr<Cancellable>& cancellable)
 : IOSource(
     g_socket_create_source(socket, (GIOCondition)condition, Glib::unwrap(cancellable)),
-    giomm_socketsource_cb_as_gsourcefunc())
+    (GSourceFunc)&giomm_socketsource_callback)
 {
 }
 
diff --git a/glib/glibmm/main.cc b/glib/glibmm/main.cc
index eec2b1cc..7edb8f41 100644
--- a/glib/glibmm/main.cc
+++ b/glib/glibmm/main.cc
@@ -242,19 +242,6 @@ glibmm_iosource_callback(GIOChannel*, GIOCondition condition, void* data)
   return 0;
 }
 
-GSourceFunc glibmm_iosource_cb_as_gsourcefunc()
-{
-  // Conversion between different types of function pointers with
-  // reinterpret_cast can make gcc8 print a warning.
-  // https://github.com/libsigcplusplus/libsigcplusplus/issues/1
-  union {
-    GSourceFunc ps;
-    decltype(&glibmm_iosource_callback) pios;
-  } u;
-  u.pios = &glibmm_iosource_callback;
-  return u.ps;
-}
-
 /* Only used by SignalChildWatch::connect().
  * These don't use Glib::Source, to avoid the unnecessary overhead
  * of a completely unused wrapper object.
@@ -520,12 +507,9 @@ SignalChildWatch::connect(const sigc::slot<void(GPid, int)>& slot, GPid pid, int
   if (priority != G_PRIORITY_DEFAULT)
     g_source_set_priority(source, priority);
 
-  union {
-    GSourceFunc ps;
-    decltype(&glibmm_child_watch_callback) pcw;
-  } u;
-  u.pcw = &glibmm_child_watch_callback;
-  g_source_set_callback(source, u.ps, conn_node, &glibmm_source_destroy_notify_callback);
+  g_source_set_callback(source, (GSourceFunc)&glibmm_child_watch_callback,
+    conn_node,
+    &glibmm_source_destroy_notify_callback);
 
   conn_node->install(source);
   g_source_attach(source, context_);
@@ -1247,13 +1231,13 @@ IOSource::IOSource(PollFD::fd_t fd, IOCondition condition) : poll_fd_(fd, condit
 
 IOSource::IOSource(const Glib::RefPtr<IOChannel>& channel, IOCondition condition)
 : Source(g_io_create_watch(channel->gobj(), (GIOCondition)condition),
-    glibmm_iosource_cb_as_gsourcefunc())
+    (GSourceFunc)&glibmm_iosource_callback)
 {
 }
 
 IOSource::IOSource(GIOChannel* channel, IOCondition condition)
 : Source(g_io_create_watch(channel, (GIOCondition)condition),
-    glibmm_iosource_cb_as_gsourcefunc())
+    (GSourceFunc)&glibmm_iosource_callback)
 {
 }
 
diff --git a/tests/giomm_stream_vfuncs/main.cc b/tests/giomm_stream_vfuncs/main.cc
index ad42e989..df1cde20 100644
--- a/tests/giomm_stream_vfuncs/main.cc
+++ b/tests/giomm_stream_vfuncs/main.cc
@@ -160,7 +160,7 @@ int main(int, char**)
       return EXIT_FAILURE;
     }
   }
-  catch (const Gio::Error& e)
+  catch (Gio::Error e)
   {
     std::cout << "Gio error: " << e.what() << std::endl;
     return EXIT_FAILURE;
diff --git a/tests/glibmm_vector/main.cc b/tests/glibmm_vector/main.cc
index 0f039356..31138cf0 100644
--- a/tests/glibmm_vector/main.cc
+++ b/tests/glibmm_vector/main.cc
@@ -196,23 +196,14 @@ public:
 
   ~Cache()
   {
-    // Conversion between different types of function pointers with
-    // reinterpret_cast can make gcc8 print a warning.
-    // https://github.com/libsigcplusplus/libsigcplusplus/issues/1
-    union {
-      GFunc pf;
-      decltype(&g_object_unref) pou;
-    } u;
-    u.pou = &g_object_unref;
-
     if (glist_)
     {
-      g_list_foreach(glist_, u.pf, nullptr);
+      g_list_foreach(glist_, reinterpret_cast<GFunc>(g_object_unref), nullptr);
       g_list_free(glist_);
     }
     if (gslist_)
     {
-      g_slist_foreach(gslist_, u.pf, nullptr);
+      g_slist_foreach(gslist_, reinterpret_cast<GFunc>(g_object_unref), nullptr);
       g_slist_free(gslist_);
     }
     if (garray_)