Index: GBoxed.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/GBoxed.xs,v
retrieving revision 1.24
diff -u -d -p -r1.24 GBoxed.xs
--- GBoxed.xs	13 Sep 2006 14:53:27 -0000	1.24
+++ GBoxed.xs	18 Nov 2007 19:54:51 -0000
@@ -462,7 +462,7 @@ gperl_get_boxed_check (SV * sv, GType gt
 	BoxedInfo * boxed_info;
 	GPerlBoxedUnwrapFunc unwrap;
 
-	if (!sv || !SvOK (sv))
+	if (!gperl_sv_defined (sv))
 		croak ("variable not allowed to be undef where %s is wanted",
 		       g_type_name (gtype));
 
@@ -556,7 +556,7 @@ strv_unwrap (GType        gtype,
 	gchar ** strv = NULL;
 
 	/* pass undef */
-	if (!sv || !SvOK (sv))
+	if (!gperl_sv_defined (sv))
 		return NULL;
 
 	if (SvROK (sv)) {
@@ -674,7 +674,7 @@ DESTROY (sv)
 	char * class;
 	GPerlBoxedDestroyFunc destroy;
     CODE:
-	if (!sv || !SvOK (sv) || !SvROK (sv) || !SvRV (sv))
+	if (!gperl_sv_defined (sv) || !SvROK (sv) || !SvRV (sv))
 		croak ("DESTROY called on a bad value");
 
 	/* we need to find the wrapper class associated with whatever type
Index: GError.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/GError.xs,v
retrieving revision 1.11
diff -u -d -p -r1.11 GError.xs
--- GError.xs	23 Jul 2006 10:20:59 -0000	1.11
+++ GError.xs	18 Nov 2007 19:54:51 -0000
@@ -219,8 +219,9 @@ gperl_gerror_from_sv (SV * sv, GError **
 	 * side effect, 0 is also allowed.  we just won't advertise that.
 	 * the logic here is a bit ugly to avoid running the overloaded
 	 * stringification operator via SvTRUE(). */
-	if (!sv || !SvOK (sv) || /* not defined */
-	    (!SvROK (sv) && !SvTRUE (sv))) { /* not a ref, but still false */
+	if (!gperl_sv_defined (sv) ||		/* not defined */
+	    (!SvROK (sv) && !SvTRUE (sv)))	/* not a ref, but still false */
+	{
 		*error = NULL;
 		return;
 	}
@@ -243,7 +244,7 @@ gperl_gerror_from_sv (SV * sv, GError **
 		const char * domain;
 		GQuark qdomain;
 		svp = hv_fetch (hv, "domain", 6, FALSE);
-		if (!svp || !SvOK (sv))
+		if (!svp || !gperl_sv_defined (*svp))
 			g_error ("key 'domain' not found in plain hash for GError");
 		domain = SvPV_nolen (*svp);
 		qdomain = g_quark_try_string (domain);
@@ -262,11 +263,11 @@ gperl_gerror_from_sv (SV * sv, GError **
 	 * error code.  prefer the 'value' key, fall back to 'code'.
 	 */
 	svp = hv_fetch (hv, "value", 5, FALSE);
-	if (svp && SvOK (*svp))
+	if (svp && gperl_sv_defined (*svp))
 		scratch.code = gperl_convert_enum (info->error_enum, *svp);
 	else {
 		svp = hv_fetch (hv, "code", 4, FALSE);
-		if (!svp || !SvOK (*svp))
+		if (!svp || !gperl_sv_defined (*svp))
 			croak ("error hash contains neither a 'value' nor 'code' key; no error valid error code found");
 		scratch.code = SvIV (*svp);
 	}
@@ -275,7 +276,7 @@ gperl_gerror_from_sv (SV * sv, GError **
 	 * the message is the easy part.
 	 */
 	svp = hv_fetch (hv, "message", 7, FALSE);
-	if (!svp || !SvOK (*svp))
+	if (!svp || !gperl_sv_defined (*svp))
 		croak ("error has contains no error message");
 	scratch.message = SvGChar (*svp);
 
Index: GObject.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/GObject.xs,v
retrieving revision 1.70
diff -u -d -p -r1.70 GObject.xs
--- GObject.xs	8 Oct 2007 19:38:44 -0000	1.70
+++ GObject.xs	18 Nov 2007 19:54:52 -0000
@@ -772,7 +772,7 @@ gperl_get_object (SV * sv)
 {
 	MAGIC *mg;
 
-	if (!sv || !SvOK (sv) || !SvROK (sv) || !(mg = mg_find (SvRV (sv), PERL_MAGIC_ext)))
+	if (!gperl_sv_defined (sv) || !SvROK (sv) || !(mg = mg_find (SvRV (sv), PERL_MAGIC_ext)))
 		return NULL;
 	return (GObject *) mg->mg_ptr;
 }
@@ -1283,8 +1283,7 @@ g_object_find_property (object_or_class_
 	GType type = G_TYPE_INVALID;
 	gchar *name = NULL;
     PPCODE:
-	if (object_or_class_name &&
-	    SvOK (object_or_class_name) &&
+	if (gperl_sv_defined (object_or_class_name) &&
 	    SvROK (object_or_class_name)) {
 		GObject * object = SvGObject (object_or_class_name);
 		if (!object)
Index: GSignal.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/GSignal.xs,v
retrieving revision 1.28
diff -u -d -p -r1.28 GSignal.xs
--- GSignal.xs	7 Aug 2006 18:17:19 -0000	1.28
+++ GSignal.xs	18 Nov 2007 19:54:52 -0000
@@ -390,8 +390,7 @@ get_gtype_or_croak (SV * object_or_class
 {
 	GType gtype;
 
-	if (object_or_class_name &&
-	    SvOK (object_or_class_name) &&
+	if (gperl_sv_defined (object_or_class_name) &&
 	    SvROK (object_or_class_name)) {
 		GObject * object = SvGObject (object_or_class_name);
 		if (!object)
Index: GType.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/GType.xs,v
retrieving revision 1.79
diff -u -d -p -r1.79 GType.xs
--- GType.xs	28 Oct 2007 22:06:36 -0000	1.79
+++ GType.xs	18 Nov 2007 19:54:53 -0000
@@ -1103,7 +1103,7 @@ parse_signal_hash (GType instance_type,
 	PERL_UNUSED_VAR (signal_name);
 
 	svp = hv_fetch (hv, "flags", 5, FALSE);
-	if (svp && (*svp) && SvOK (*svp))
+	if (svp && gperl_sv_defined (*svp))
 		s->flags = SvGSignalFlags (*svp);
 
 	svp = hv_fetch (hv, "param_types", 11, FALSE);
@@ -1126,7 +1126,7 @@ parse_signal_hash (GType instance_type,
 
 	svp = hv_fetch (hv, "class_closure", 13, FALSE);
 	if (svp && *svp) {
-		if (SvOK (*svp))
+		if (gperl_sv_defined (*svp))
 			s->class_closure =
 				gperl_closure_new (*svp, NULL, FALSE);
 		/* else the class closure is NULL */
@@ -1135,7 +1135,7 @@ parse_signal_hash (GType instance_type,
 	}
 
 	svp = hv_fetch (hv, "return_type", 11, FALSE);
-	if (svp && (*svp) && SvOK (*svp)) {
+	if (svp && gperl_sv_defined (*svp)) {
 		s->return_type = gperl_type_from_package (SvPV_nolen (*svp));
 		if (!s->return_type)
 			croak ("unknown or unregistered return type %s",
@@ -1430,9 +1430,8 @@ add_interfaces (GType instance_type, AV 
 
         for (i = 0; i <= av_len (interfaces); i++) {
 		SV ** svp = av_fetch (interfaces, i, FALSE);
-		if (!svp && !SvOK (*svp))
-			croak ("%s is not a valid interface name",
-			       SvPV_nolen (*svp));
+		if (!svp || !gperl_sv_defined (*svp))
+			croak ("encountered invalid interface name");
 
 		/* call the interface's setup function on this class. */
 		{
@@ -2287,16 +2286,16 @@ g_type_register_enum (class, name, ...)
 			AV * av = (AV*)SvRV(sv);
 			/* value_name */
 			av2sv = av_fetch (av, 0, 0);
-			if (av2sv && *av2sv && SvOK(*av2sv))
+			if (av2sv && gperl_sv_defined (*av2sv))
 				values[i].value_name = SvPV_nolen (*av2sv);
 			else
 				croak ("invalid enum name and value pair, no name provided");
 			/* custom value */
 			av2sv = av_fetch (av, 1, 0);
-			if (av2sv && *av2sv && SvOK(*av2sv))
+			if (av2sv && gperl_sv_defined (*av2sv))
 				values[i].value = SvIV (*av2sv);
 		}
-		else if (SvOK (sv))
+		else if (gperl_sv_defined (sv))
 		{
 			/* name syntax */
 			values[i].value_name = SvPV_nolen (sv);
@@ -2373,16 +2372,16 @@ g_type_register_flags (class, name, ...)
 			AV * av = (AV*)SvRV(sv);
 			/* value_name */
 			av2sv = av_fetch (av, 0, 0);
-			if (av2sv && *av2sv && SvOK(*av2sv))
+			if (av2sv && gperl_sv_defined (*av2sv))
 				values[i].value_name = SvPV_nolen (*av2sv);
 			else
 				croak ("invalid flag name and value pair, no name provided");
 			/* custom value */
 			av2sv = av_fetch (av, 1, 0);
-			if (av2sv && *av2sv && SvOK(*av2sv))
+			if (av2sv && gperl_sv_defined (*av2sv))
 				values[i].value = SvIV (*av2sv);
 		}
-		else if (SvOK (sv))
+		else if (gperl_sv_defined (sv))
 		{
 			/* name syntax */
 			values[i].value_name = SvPV_nolen (sv);
Index: GValue.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/GValue.xs,v
retrieving revision 1.20
diff -u -d -p -r1.20 GValue.xs
--- GValue.xs	13 Nov 2005 16:43:43 -0000	1.20
+++ GValue.xs	18 Nov 2007 19:54:53 -0000
@@ -66,7 +66,7 @@ gperl_value_from_sv (GValue * value,
 {
 	char* tmp;
 	GType type;
-	if (!sv || !SvOK (sv))
+	if (!gperl_sv_defined (sv))
 		return TRUE; /* use the GValue type's default */
 	type = G_TYPE_FUNDAMENTAL (G_VALUE_TYPE (value));
 	/*printf ("TYPE: %d, S: %s\n", type, SvPV_nolen(sv));*/
@@ -125,7 +125,7 @@ gperl_value_from_sv (GValue * value,
 			/* SVs need special treatment! */
 			if (G_VALUE_HOLDS (value, GPERL_TYPE_SV))
 				g_value_set_boxed (value,
-				                   sv && SvOK (sv) 
+				                   gperl_sv_defined (sv)
 				                   ? sv : NULL);
 			else
 				g_value_set_boxed (value, gperl_get_boxed_check (sv, G_VALUE_TYPE(value)));
Index: Glib.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/Glib.xs,v
retrieving revision 1.49
diff -u -d -p -r1.49 Glib.xs
--- Glib.xs	30 Dec 2006 15:37:17 -0000	1.49
+++ Glib.xs	18 Nov 2007 19:54:53 -0000
@@ -230,10 +230,10 @@ gperl_argv_new ()
 	pargv->argv[0] = SvPV_nolen (ARGV0);
 
 	for (i = 0 ; i < len ; i++) {
-		SV ** sv = av_fetch (ARGV, i, 0);
-		if (sv && SvOK (*sv))
+		SV ** svp = av_fetch (ARGV, i, 0);
+		if (svp && gperl_sv_defined (*svp))
 			pargv->shadow[i] = pargv->argv[i+1]
-			                 = g_strdup (SvPV_nolen (*sv));
+			                 = g_strdup (SvPV_nolen (*svp));
 	}
 
 	return pargv;
@@ -283,7 +283,7 @@ gperl_format_variable_for_output (SV * s
 {
 	if (sv) {
 		/* disambiguate undef */
-		if (!SvOK (sv))
+		if (!gperl_sv_defined (sv))
 			return SvPV_nolen (sv_2mortal (newSVpv ("undef", 5)));
 		/* don't truncate references... */
 		if (SvROK (sv))
@@ -297,6 +297,39 @@ gperl_format_variable_for_output (SV * s
 	return NULL;
 }
 
+gboolean
+gperl_sv_defined (SV *sv)
+{
+	/* This is adapted from PP(pp_defined) in perl's pp.c */
+
+	if (!sv || !SvANY(sv))
+		return FALSE;
+
+	switch (SvTYPE(sv)) {
+	    case SVt_PVAV:
+		if (AvMAX(sv) >= 0 || SvGMAGICAL(sv)
+		    || (SvRMAGICAL(sv) && mg_find(sv, PERL_MAGIC_tied)))
+			return TRUE;
+		break;
+	    case SVt_PVHV:
+		if (HvARRAY(sv) || SvGMAGICAL(sv)
+		    || (SvRMAGICAL(sv) && mg_find(sv, PERL_MAGIC_tied)))
+			return TRUE;
+		break;
+	    case SVt_PVCV:
+		if (CvROOT(sv) || CvXSUB(sv))
+			return TRUE;
+		break;
+	    default:
+		if (SvGMAGICAL(sv))
+			mg_get(sv);
+		if (SvOK(sv))
+			return TRUE;
+	}
+
+	return FALSE;
+}
+
 =back
 
 =cut
@@ -430,10 +463,10 @@ filename_to_uri (...)
     CODE:
 	if (items == 2) {
 		filename = SvPV_nolen (ST (0));
-		hostname = SvOK (ST (1)) ? SvPV_nolen (ST (1)) : NULL;
+		hostname = gperl_sv_defined (ST (1)) ? SvPV_nolen (ST (1)) : NULL;
 	} else if (items == 3) {
 		filename = SvPV_nolen (ST (1));
-		hostname = SvOK (ST (2)) ? SvPV_nolen (ST (2)) : NULL;
+		hostname = gperl_sv_defined (ST (2)) ? SvPV_nolen (ST (2)) : NULL;
 	} else {
 		croak ("Usage: Glib::filename_to_uri (filename, hostname)\n"
 		       " -or-  Glib->filename_to_uri (filename, hostname)\n"
Index: gperl.h
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Glib/gperl.h,v
retrieving revision 1.49
diff -u -d -p -r1.49 gperl.h
--- gperl.h	15 Sep 2007 14:10:12 -0000	1.49
+++ gperl.h	18 Nov 2007 19:54:53 -0000
@@ -76,6 +76,8 @@ void gperl_argv_free (GPerlArgv *pargv);
 
 char * gperl_format_variable_for_output (SV * sv);
 
+gboolean gperl_sv_defined (SV *sv);
+
 /* internal trickery */
 gpointer gperl_type_class (GType type);
 /*
Index: t/tied_properties.t
===================================================================
RCS file: t/tied_properties.t
diff -N t/tied_properties.t
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ t/tied_properties.t	18 Nov 2007 19:54:53 -0000
@@ -0,0 +1,57 @@
+#!/usr/bin/perl
+
+package ClassFoo;
+use strict;
+use warnings;
+use Glib;
+
+use Glib::Object::Subclass
+  Glib::Object::,
+  properties => [
+    Glib::ParamSpec->boxed('title',
+                           'title',
+                           'The title',
+                           'Glib::Scalar',
+                           [qw/writable readable/]),
+  ];
+
+sub INIT_INSTANCE {
+    my $self = shift;
+    $self->{prop_title} = undef;
+}
+
+sub SET_PROPERTY {
+    my ($self, $pspec, $val) = @_;
+    my $propname = $pspec->get_name;
+    if ($propname eq 'title') {
+        $self->{prop_title} = $val;
+    } else {
+        die "unknown property ``$propname''";
+    }
+}
+
+sub GET_PROPERTY {
+    my ($self, $pspec) = @_;
+    my $propname = $pspec->get_name;
+    if ($propname eq 'title') {
+        return $self->{prop_title};
+    } else {
+        die "unknown property ``$propname''";
+    }
+}
+
+# --------------------------------------------------------------------------- #
+
+package main;
+use strict;
+use warnings;
+use Tie::Hash;
+use Test::More tests => 1;
+
+my $hashref = {};
+tie %$hashref, 'Tie::StdHash';
+$hashref->{Title} = 'foo';
+
+my $w = ClassFoo->new;
+$w->set_property ('title', $hashref->{Title});
+is ($w->get_property ('title'), $hashref->{Title});