example.swift

typealias Callback = () -> ()

// Both methods are required
class Something {
   var calledOnce:Callback?
   var calledMultipleTimes:Callback?
}

Here ya go:

class SomeUsefulProcessDelinquent<InputType, ResultType> {
    typealias CallMeWhenYouWannaMapMe = (InputType) -> ResultType
    typealias CallMeWhenYouWannaChangeMe = ([InputType]) -> [ResultType]

    let mapClosure : CallMeWhenYouWannaMapMe
    let updateClosure : CallMeWhenYouWannaChangeMe

    init(mapFunction : CallMeWhenYouWannaMapMe, updateFunction : CallMeWhenYouWannaChangeMe) {
        self.mapClosure = mapFunction
        self.updateClosure = updateFunction
    }
}