 The callback
function pointer is no longer valid and must not be called anymore
(it may be reused by a subsequently created callback).
</p>

<h3 id="callback_set"><tt>cb:set(func)</tt></h3>
<p>
Associate a new Lua function with a callback. The C&nbsp;type of the
callback and the callback function pointer are unchanged.
</p>
<p>
This method is useful to dynamically switch the receiver of callbacks
without creating a new callback each time and registering it again (e.g.
with a GUI library).
</p>

<h2 id="ext