[glibmm/glibmm-2-56] Revert "Avoid compiler warnings from function pointer conversions"

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 9e457844f544793ab2b727351fca0805ddc0c20a
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Tue Jul 17 16:43:30 2018 +0200

    Revert "Avoid compiler warnings from function pointer conversions"
    
    This reverts commit 5d953603f30f0452cb9da35e3083a3fc145c3f57.
    
    This can be done in a better way by keeping the union in a template function.

 gio/giomm/socketsource.cc   | 24 +++---------------------
 glib/glibmm/main.cc         | 23 +++--------------------
 tests/glibmm_vector/main.cc | 13 ++-----------
 3 files changed, 8 insertions(+), 52 deletions(-)
---
diff --git a/gio/giomm/socketsource.cc b/gio/giomm/socketsource.cc
index 8bad8f5b..af1e9740 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
@@ -114,7 +96,7 @@ 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)
 {
 }
 
diff --git a/glib/glibmm/main.cc b/glib/glibmm/main.cc
index 45ba817e..30a294c4 100644
--- a/glib/glibmm/main.cc
+++ b/glib/glibmm/main.cc
@@ -278,19 +278,6 @@ 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.
@@ -553,12 +540,8 @@ 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, &SourceConnectionNode::destroy_notify_callback);
+  g_source_set_callback(source, (GSourceFunc)&glibmm_child_watch_callback, conn_node,
+    &SourceConnectionNode::destroy_notify_callback);
 
   conn_node->install(source);
   g_source_attach(source, context_);
@@ -1326,7 +1309,7 @@ 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)
 {
 }
 
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_)