I might have gone a bit overboard with the type-checking, but
typesafe_cb_cast is quite nice to use, so why not. The macro to
register a new hook encapsulates the entire flow from param
serialization, to dispatch, parsing and callback dispatch in one
bundle. I was tempted to have the callback outside of the
registration, but it's unlikely that we'll have two calls to the same
hook with different callbacks.
Signed-off-by: Christian Decker <decker.christian@gmail.com>
