Decreases the reference count of object. When its reference count drops to 0, the object is finalized (i.e. its memory is freed).

If the pointer to the GObject may be reused in future (for example, if it is an instance variable of another object), it is recommended to clear the pointer to NULL rather than retain a dangling pointer to a potentially invalid GObject instance. Use g_clear_object() for this.

class ObjectG