cal count = 0
ffi.C.EnumWindows(function(hwnd, l)
  count = count + 1
  return true
end, 0)
-- The callback is permanent and its resources cannot be reclaimed!
-- Ok, so this may not be a problem, if you do this only once.
</pre>
<p>
Note: this example shows that you <em>must</em> properly declare
<tt>__stdcall</tt> callbacks on Windows/x86 systems. The calling
convention cannot be automatically detected, unlike for
<tt>__stdcall</tt> calls <em>to</em> Windows functions.
</p>
<p>
For some use cases it's nec