SignalEmissionHook  
    typealias SignalEmissionHook = (ihint: SignalInvocationHint, <Error class: unknown class>, <Error class: unknown class>?) -> Boolean(source)
A simple function pointer to get invoked when the signal is emitted.
Emission hooks allow you to tie a hook to the signal type, so that it will trap all emissions of that signal, from any object.
You may not attach these to signals created with the %G_SIGNAL_NO_HOOKS flag.
- param - ihintSignal invocation hint, see #GSignalInvocationHint.
- param - nParamValuesthe number of parameters to the function, including the instance on which the signal was emitted.
- param - datauser data associated with the hook.
- return whether it wants to stay connected. If it returns false, the signal hook is disconnected (and destroyed).