Squashed commit of the following:

commit 7f46be64521d7cdf4d94409f979143a55acd665a
Author: Avi Zimmerman <avi.zimmerman@gmail.com>
Date:   Thu Jan 7 12:18:37 2021 +0200

    improve plugin interfaces

gst/g_object.go

@@ -0,0 +1,78 @@
+package gst
+
+/*
+#include "gst.go.h"
+
+extern void            goObjectSetProperty  (GObject * object, guint property_id, const GValue * value, GParamSpec *pspec);
+extern void            goObjectGetProperty  (GObject * object, guint property_id, GValue * value, GParamSpec * pspec);
+extern void            goObjectConstructed  (GObject * object);
+extern void            goObjectFinalize     (GObject * object, gpointer klass);
+
+void objectFinalize (GObject * object)
+{
+	GObjectClass *parent = g_type_class_peek_parent((G_OBJECT_GET_CLASS(object)));
+	goObjectFinalize(object, G_OBJECT_GET_CLASS(object));
+	parent->finalize(object);
+}
+
+void objectConstructed (GObject * object)
+{
+	GObjectClass *parent = g_type_class_peek_parent((G_OBJECT_GET_CLASS(object)));
+	goObjectConstructed(object);
+	parent->constructed(object);
+}
+
+void  setGObjectClassSetProperty  (void * klass)  { ((GObjectClass *)klass)->set_property = goObjectSetProperty; }
+void  setGObjectClassGetProperty  (void * klass)  { ((GObjectClass *)klass)->get_property = goObjectGetProperty; }
+void  setGObjectClassConstructed  (void * klass)  { ((GObjectClass *)klass)->constructed = objectConstructed; }
+void  setGObjectClassFinalize     (void * klass)  { ((GObjectClass *)klass)->finalize = objectFinalize; }
+
+*/
+import "C"
+import (
+	"unsafe"
+
+	"github.com/gotk3/gotk3/glib"
+)
+
+// GoObject is an interface that abstracts on the GObject. In most cases at least SetProperty and GetProperty
+// should be implemented by elements built from the go bindings.
+type GoObject interface {
+	// SetProperty should set the value of the property with the given id. ID is the index+1 of the parameter
+	// in the order it was registered.
+	SetProperty(obj *Object, id uint, value *glib.Value)
+	// GetProperty should retrieve the value of the property with the given id. ID is the index+1 of the parameter
+	// in the order it was registered.
+	GetProperty(obj *Object, id uint) *glib.Value
+	// Constructed is called when the Object has finished setting up.
+	Constructed(*Object)
+}
+
+// ExtendsObject signifies a GoElement that extends a GObject.
+var ExtendsObject Extendable = &extendObject{}
+
+type extendObject struct{}
+
+func (e *extendObject) Type() glib.Type     { return glib.Type(C.g_object_get_type()) }
+func (e *extendObject) ClassSize() int64    { return int64(C.sizeof_GObjectClass) }
+func (e *extendObject) InstanceSize() int64 { return int64(C.sizeof_GObject) }
+
+func (e *extendObject) InitClass(klass unsafe.Pointer, elem GoElement) {
+	C.setGObjectClassFinalize(klass)
+
+	if _, ok := elem.(interface {
+		SetProperty(obj *Object, id uint, value *glib.Value)
+	}); ok {
+		C.setGObjectClassSetProperty(klass)
+	}
+	if _, ok := elem.(interface {
+		GetProperty(obj *Object, id uint) *glib.Value
+	}); ok {
+		C.setGObjectClassGetProperty(klass)
+	}
+	if _, ok := elem.(interface {
+		Constructed(*Object)
+	}); ok {
+		C.setGObjectClassConstructed(klass)
+	}
+}