Issuing Landing Instructions

We've implemented the runway, terminal, and gate lodging. 0:01 So let's tie it all together in land method of the control tower, 0:04 which is down here. 0:08 Earlier, when we implemented the logic for the terminal enum, we simply returned 0:11 enum members with the associated values set to nil as a temporary workaround. 0:16 So let me actually scroll back up to Terminal for a second. 0:21 And over here, you can see we're simply returning A and nil values, 0:24 no actual gate numbers. 0:27 To fix this, now we can go back in and enter a couple lines of code for 0:29 each case in the switch statement. 0:33 So if it's a domestic airline and more specifically, 0:35 it's a Delta flight, let's get a gate for Terminal A. 0:38 So we could say let gate = GateManager.sharedInstance.gateFor and 0:42 we'll say Terminal A. 0:52 Now this returns a integer value as the gate, so we can use that in here. 0:56 When we specify the terminal for the GateManager's instance method, 1:02 we just pass in nil for the associated value to satisfy the compiler. 1:06 We don't really have a gate number at this point. 1:10 With the gate value we get back, 1:13 we assign this as an associated value to the relevant enum member and return it. 1:14 So let's repeat this process for every airline. 1:20 So we'll say let gate, I can just copy this. 1:23 And, let me go change everything so 1:34 this is B, this is C, this is International, 1:39 and the last one is Private. 1:46 And then finally, we need to use that gate as an associated value. 1:53 Now you could modify the gateFor terminal that's this method over here 2:01 you could modify this method to return a terminal value instead of just an integer. 2:06 That should allow you to clean up the terminal logic as well and 2:13 eliminate a lot of repeated code. 2:16 Now, I haven't done that specifically, 2:19 because I want you to try it out as a refactoring exercise. 2:21 No guidance, just try and improve this code on your own. 2:25 Okay, with that done, let's head back down to the land method. 2:29 We already have the runway over here, so all we need is the terminal. 2:33 So we can say let terminal=Terminal.terminal and 2:38 we'll pass in the airline, super simple. 2:44 The airline protocol encodes the type information and we can cast the type to 2:48 a more specific type and figure out things, all of this we've already done. 2:53 So let's add a terminal store property to the landing instruction struct now that we 2:58 have it, so that we can return it. 3:03 So we'll say let terminal, and just like the type for 3:04 runway, since this is a nested type, we'll say ControlTower.terminal. 3:09 Okay, let's go back down. 3:15 There's an error and that's because I need to return the terminal. 3:16 Take a step back and inspect your code. 3:22 Make sure you really understand things because 3:25 we've pretty much implemented all the logic for our control tower 3:27 by relying on the information encoded in the Airline protocol. 3:31 We do have enums that indicate what different airlines we can expect to land, 3:35 but we didn't need to create an instance of, 3:41 say, domestic airline to get this to work. 3:43 But finally, with all of this out of the way, 3:46 let's now focus on creating the type that we will be interacting with primarily, so 3:49 the domestic airline and international airline. 3:53 Note that I'm not going to implement the private airline for 3:57 this example because it's more or less identical. 3:59 So down below the control tower, let's create a new type. 4:03 We'll say struct DomesticAirline and 4:07 remember all our airlines conform to the Airline protocol. 4:11 So we'll say Airline and open up the body. 4:16 For this narrow example, 4:19 all we need to conform to Airline is to implement three things. 4:21 So we need the descent speed, which we'll make a constant. 4:24 We need the type, which is also constant. 4:30 And finally, we need a single method which is requestLandingInstructions. 4:36 Now the body of this method is all too simple, all we're going to say is return 4:42 ControlTower.land, and we'll pass in self. 4:47 So over here, we're just asking the ControlTower for landing instructions. 4:54 Whoops, we need that, there we go. 4:59 Now similarly, we could implement the international flight type, 5:01 but that's not even necessary because it's almost identical. 5:05 We can change this name and it's exactly the same. 5:09 Most of the work is being done by the Airline protocol, 5:12 so we really don't need to have anything in here. 5:15 Ignoring the fact that in a more complex example, 5:18 there would be more differences between domestic and 5:21 international flights, in our case it's nearly identical. 5:23 I could change the struct name like I just mentioned, and 5:28 we really wouldn't have to change anything else. 5:30 This indicates, if you think about it, that we may not even need these types. 5:33 We may not need DomesticAirlines and InternationalAirlines separately. 5:37 Let's take a break here. 5:42 And in the next video, we'll explore how protocols can help the situation further. 5:43