‘RestKit’ comes with great support for asynchronous invocations that complete in a block. My recent experience with Node.js lead to me adopting a pattern, that Swift with its modern clean syntax, makes a snip to use.

The chain of actions that I need to perform to get the status for the users home location is:

• Find their current location
• Find the Home station (closest of their favorite stations
• Get the status of all lines
• Process the status and return the data to the watch

Let’s use an action in the chain to demonstrate the pattern. If we look at the HomeStaionFinder class:

 func find(#andThen: (TBStation) -> () ) {
        TBLInes.sharedInstance().updateDistances(location)
        andThen(TBLInes.sharedInstance().stationsOrderedByDistance().first);
    }

This code is elided but should show the gist of it. What makes the whole thing really pleasant to use and easy to read is the continuation method andThen: passed in as a parameter. When these classes are chained together we get:

 func collect( finally: (HomePageData) -> () ) {
    LocationFinder(waitFor: 1).find( andThen: { (location) -> () in
        HomeStationFinder(from:location).find(andThen: { (home) -> () in
            StatusFinder().find(andThen: { () -> () in
                finally(self.collectedData);
            })
        })
    })
}
    

I think I’m going to like Swift.