1 00:00:00,780 --> 00:00:04,320 In this video, I want to show you a couple of different diagrams to help you really understand what 2 00:00:04,320 --> 00:00:08,430 is going on inside this file and really understand what the goal of the interface is right here. 3 00:00:08,460 --> 00:00:09,380 So let's get to it. 4 00:00:10,340 --> 00:00:13,850 All right, on the left hand side, at the very bottom, we've got that print summary function that 5 00:00:13,850 --> 00:00:14,690 we just put together. 6 00:00:15,690 --> 00:00:21,510 We can kind of think of that interface that we are using to annotate the argument to that function as 7 00:00:21,510 --> 00:00:23,420 being like a gatekeeper of sorts. 8 00:00:24,060 --> 00:00:28,470 In other words, if we ever have any value inside of our application, like, say, old civic or drink 9 00:00:28,470 --> 00:00:34,170 over here, and we want to use these values with a summary function, we have to make sure that those 10 00:00:34,170 --> 00:00:37,290 values implement the reportable interface. 11 00:00:37,920 --> 00:00:42,210 In other words, these two values have to have a summary function that returns a string. 12 00:00:42,810 --> 00:00:45,840 If they don't, then they cannot be used with print summary. 13 00:00:47,280 --> 00:00:52,620 This mechanic right here of using an interface for gatekeeping is going to be one of the prime ways 14 00:00:52,620 --> 00:00:57,600 that we get some amount of code reuse inside of TypeScript, and you're going to see the strategy used 15 00:00:57,600 --> 00:01:01,350 over and over in every application we put together in this course. 16 00:01:02,370 --> 00:01:07,440 So the general strategy that we're going to use for code reuse in typescript is to create functions 17 00:01:07,680 --> 00:01:11,340 that accept arguments that are typed with interfaces. 18 00:01:12,340 --> 00:01:17,740 So all the different functions we're going to create are going to accept interfaces as much as possible, 19 00:01:17,920 --> 00:01:22,840 obviously not every last function we ever put together is always going to require an interface type 20 00:01:22,840 --> 00:01:23,290 argument. 21 00:01:23,500 --> 00:01:28,360 Sometimes we're going to have something that takes a string or a boolean or maybe a plain object in 22 00:01:28,360 --> 00:01:30,100 some far off cases. 23 00:01:30,520 --> 00:01:35,530 But in general, we're going to try to create functions that accept arguments that are typed with interfaces. 24 00:01:36,350 --> 00:01:42,080 And then in order to call those functions, we're going to make sure that we have objects or classes 25 00:01:42,440 --> 00:01:45,290 that can decide to implement that interface. 26 00:01:46,620 --> 00:01:51,630 So it's essentially this same scenario right over here, we created a function that takes an interface 27 00:01:51,630 --> 00:01:58,200 type as an argument, so other values inside of our application can opt into satisfying or implementing 28 00:01:58,200 --> 00:02:00,270 that interface to work with that function. 29 00:02:01,560 --> 00:02:05,850 This diagram that you're seeing right here, we can kind of generalize into something like this so we 30 00:02:05,850 --> 00:02:10,830 can imagine some like arbitrary interface over here that's going to govern access to some function. 31 00:02:11,100 --> 00:02:16,100 And if we want to work with this function, any other object must implement that interface. 32 00:02:16,740 --> 00:02:20,940 So we're going to see this exact diagram right here in many other applications we work on. 33 00:02:21,090 --> 00:02:23,610 And every single time, it's going to have the exact same meaning. 34 00:02:23,610 --> 00:02:26,160 We're going to talk about how we've got some function. 35 00:02:26,160 --> 00:02:32,400 And in order to call it we, we must have some values that implement the given interface that's acting 36 00:02:32,400 --> 00:02:33,450 as the gatekeeper. 37 00:02:34,480 --> 00:02:38,440 All right, so at this point, I'm sure this is still a little bit confusing, but like I said earlier, 38 00:02:38,590 --> 00:02:43,810 the good news is that the entire course, like every application we put together, is going to be focusing 39 00:02:43,810 --> 00:02:45,670 100 percent on this mechanic. 40 00:02:46,210 --> 00:02:51,460 We're going to be focusing on how to define different interfaces, to restrict access to different functions 41 00:02:51,910 --> 00:02:56,710 and then decide how to implement those different interfaces in different objects that are going to create. 42 00:02:57,580 --> 00:03:01,900 So the real code we use, we're going to get here is making essentially this function right here really 43 00:03:01,900 --> 00:03:02,530 reusable. 44 00:03:02,830 --> 00:03:06,700 As long as a value implements that interface, it can work with this function. 45 00:03:07,510 --> 00:03:07,810 All right. 46 00:03:07,810 --> 00:03:09,030 So let's take a quick pause right here. 47 00:03:09,160 --> 00:03:11,260 We're going to move on to our next topic in the next video.