Add optional callbacks to xas_object

Changes:

    * Implement xas_object_init() to initialise an object call table
      to all null values

    * Rework dispatch methods to fail gracefully if no pointer value is
      provided for a given callback entry

Additional changes:

    * Add callbacks for changing bank and frequency

2 files changed, 66 insertions, 1 deletions

diff --git a/include/xas/object.h b/include/xas/object.h
index a164277..4392892 100644
--- a/include/xas/object.h
+++ b/include/xas/object.h
@@ -11,6 +11,10 @@ typedef int (*xas_object_stop_callback)(xas_object *object);
 
 typedef int (*xas_object_set_gain_callback)(xas_object *object, float gain);
 
+typedef int (*xas_object_set_freq_callback)(xas_object *object, size_t freq);
+
+typedef int (*xas_object_set_bank_callback)(xas_object *object, size_t gain);
+
 typedef xas_audio_stream *(*xas_object_stream_new_callback)(xas_object *object);
 
 typedef void (*xas_object_destroy_callback)(xas_object *object);
@@ -19,16 +23,24 @@ struct _xas_object {
     xas_object_start_callback      start;
     xas_object_stop_callback       stop;
     xas_object_set_gain_callback   set_gain;
+    xas_object_set_bank_callback   set_bank;
+    xas_object_set_freq_callback   set_freq;
     xas_object_stream_new_callback stream_new;
     xas_object_destroy_callback    destroy;
 };
 
+void xas_object_init(xas_object *object);
+
 int xas_object_start(xas_object *object);
 
 int xas_object_stop(xas_object *object);
 
 int xas_object_set_gain(xas_object *object, float gain);
 
+int xas_object_set_bank(xas_object *object, size_t bank);
+
+int xas_object_set_freq(xas_object *object, size_t freq);
+
 xas_audio_stream *xas_object_stream_new(xas_object *object);
 
 void xas_object_destroy(xas_object *object);
diff --git a/src/object.c b/src/object.c
index 7aaaa6e..4526bc5 100644
--- a/src/object.c
+++ b/src/object.c
@@ -1,21 +1,74 @@
+#include <string.h>
+#include <errno.h>
+
 #include <xas/object.h>
 
+void xas_object_init(xas_object *object) {
+    memset(object, '\0', sizeof(xas_object));
+}
+
 int xas_object_start(xas_object *object) {
+    if (object->start == NULL) {
+        errno = ENOSYS;
+
+        return -1;
+    }
+
     return object->start(object);
 }
 
 int xas_object_stop(xas_object *object) {
+    if (object->stop == NULL) {
+        errno = ENOSYS;
+
+        return -1;
+    }
+
     return object->stop(object);
 }
 
 int xas_object_set_gain(xas_object *object, float gain) {
+    if (object->set_gain == NULL) {
+        errno = ENOSYS;
+
+        return -1;
+    }
+
     return object->set_gain(object, gain);
 }
 
+int xas_object_set_bank(xas_object *object, size_t bank) {
+    if (object->set_bank == NULL) {
+        errno = ENOSYS;
+
+        return -1;
+    }
+
+    return object->set_bank(object, bank);
+}
+
+int xas_object_set_freq(xas_object *object, size_t freq) {
+    if (object->set_freq == NULL) {
+        errno = ENOSYS;
+
+        return -1;
+    }
+
+    return object->set_freq(object, freq);
+}
+
 xas_audio_stream *xas_object_stream_new(xas_object *object) {
+    if (object->stream_new == NULL) {
+        errno = ENOSYS;
+
+        return NULL;
+    }
+
     return object->stream_new(object);
 }
 
 void xas_object_destroy(xas_object *object) {
-    object->destroy(object);
+    if (object->destroy) {
+        object->destroy(object);
+    }
 }