WEBVTT 00:00.410 --> 00:09.980 So as we talked about the abstract classes and abstract methods inside those classes, they actually 00:09.980 --> 00:11.360 have to be extended. 00:11.360 --> 00:14.030 So that's the point of an abstract class. 00:14.030 --> 00:19.670 Well, it's actually fine for an abstract class to sit around an extended. 00:19.670 --> 00:21.170 You don't really need to do that. 00:21.170 --> 00:23.570 But then there is no point of such class. 00:23.600 --> 00:33.710 But if you extend you inherit an abstract class, then you need to override those abstract methods and 00:33.710 --> 00:35.210 actually implement them. 00:35.780 --> 00:40.970 Now there is also like another side of the coin to this. 00:41.090 --> 00:48.050 So another spectrum which are final classes and final methods. 00:48.050 --> 00:56.990 And as you can guess, probably these are the classes and methods that you can't extend. 00:57.380 --> 01:01.250 So here we've got an online payment processor. 01:01.280 --> 01:09.800 An abstract class that implements an interface and it is used and it is prepared so that if there is 01:09.800 --> 01:17.270 a need to implement another payment processor except stripe and PayPal, this can be easily done. 01:17.270 --> 01:28.490 But there might be situations when maybe either PayPal or maybe stripe is introducing a new version 01:28.490 --> 01:38.150 of their system, and for some reason, someone on your team thinks it's a good idea to just extend 01:38.150 --> 01:44.450 the stripe processor and maybe call it stripe processor version two. 01:44.450 --> 01:53.210 And maybe this just changes the validate API key or any other behavior. 01:53.210 --> 02:01.130 So anyway, generally someone thinks that creating class like this is a good idea. 02:01.640 --> 02:10.730 So I would advise you against doing that and against having a complex inheritance tree. 02:10.850 --> 02:20.840 I think that inheritance works best only if you use it the way that there is an abstract class that 02:20.840 --> 02:28.580 is there to provide some functionality and show you the way of how something should be done, and then 02:28.580 --> 02:29.540 it is a good idea. 02:29.570 --> 02:37.790 Like this class is a good idea, but then endlessly extending a base class to add more and then add 02:37.820 --> 02:45.020 even more functionality, this can really end up creating a mess. 02:45.020 --> 02:53.690 And if you want to stop people from creating a mess, especially if this might be some junior coworkers, 02:53.840 --> 03:02.220 you just mark a class with the keyword final and if anyone tries this, if they want to extend it, 03:02.220 --> 03:05.160 this is just a fatal error. 03:05.460 --> 03:08.400 You cannot extend a final class. 03:08.670 --> 03:11.610 Now you can also mark methods final. 03:13.110 --> 03:17.970 So let's remove that because this was a bad idea. 03:20.430 --> 03:29.670 Now some people even default to marking the classes as final, and only if you need to extend a class. 03:29.670 --> 03:37.200 You need to then remove the final keyword and possibly also explain why you would like to do that. 03:37.230 --> 03:45.540 Now also, just keep in mind that if you really feel the urge to extend a class that's already there, 03:45.840 --> 03:54.270 just think if maybe composition isn't a better idea, because with every single class, you can actually 03:54.270 --> 03:56.100 pass it through a constructor. 03:56.100 --> 03:59.700 And that is actually a very good pattern. 04:01.170 --> 04:09.390 Now, another useful thing in modern versions of PHP are read only properties. 04:11.040 --> 04:18.570 So currently, for example, with this one we've got the constructor property promotion. 04:20.160 --> 04:27.240 So this is an API key property on this class that can also be accessed in the child classes. 04:27.270 --> 04:34.650 But if the class should be created with a key and then not modified, and you want to make sure the 04:34.650 --> 04:41.970 property is never modified, then you can add a read only keyword to it. 04:41.970 --> 04:50.370 And if anyone attempts to change the value of this property, obviously after it was initialized, this 04:50.370 --> 04:54.150 would also raise a fatal error. 04:54.480 --> 05:03.480 Now, I also think that if you are passing some data to an object, and this data is credentials, keys 05:03.480 --> 05:05.550 or anything that shouldn't change. 05:05.550 --> 05:14.130 You should default to those properties bank read only and only then try to remove read only attribute 05:14.160 --> 05:15.870 read only keyword. 05:16.260 --> 05:21.390 If actually this property should change and that's expected. 05:23.130 --> 05:30.240 Since we are talking about modern PHP features, let's also mention a union type. 05:30.810 --> 05:32.610 This is something like this. 05:34.980 --> 05:36.510 So we are using this. 05:36.540 --> 05:44.640 Let's call it a pipe operator to tell PHP that specific function argument. 05:44.730 --> 05:53.190 This also works with return types and properties that it can take different types, because previously 05:53.220 --> 05:59.970 we were limited to float and if for any reason you've got some data that was an integer. 06:00.240 --> 06:02.370 This just wouldn't work. 06:03.690 --> 06:09.750 So by using this pipe operator you can specify multiple acceptable types. 06:09.750 --> 06:13.410 You can specify as many as you want actually. 06:13.410 --> 06:19.740 But with numbers those two typically can cover most of the cases. 06:20.100 --> 06:25.290 So now after this change we should actually change that everywhere. 06:29.400 --> 06:37.830 Now the union type can also be used for accepting different kinds of values. 06:37.830 --> 06:42.600 By different I mean not just numbers that are float or integer. 06:42.630 --> 06:50.670 But you can add this type to accept maybe an array and also a string. 06:54.900 --> 07:02.230 And to show you an example of that, maybe you can have this process order function that apart from 07:02.230 --> 07:05.800 the amount can also accept items. 07:05.890 --> 07:11.770 So this can be string one item or just an array of items. 07:11.860 --> 07:14.530 So let's call that items. 07:15.790 --> 07:19.120 And here we're going to do some processing with the items. 07:19.120 --> 07:28.300 So after accepting different types of arguments you can also check what is the actual type. 07:28.660 --> 07:31.660 So we can use if is array. 07:31.870 --> 07:35.800 That's the function that will just tell us if that's an array or not. 07:35.860 --> 07:44.260 So if this is an array we can use implode to convert this to a string. 07:44.260 --> 07:47.170 So we use a comma and items. 07:49.630 --> 07:54.370 Otherwise the items list is just a string. 07:54.370 --> 07:56.740 So it is the items. 08:01.780 --> 08:05.770 And here we will always output that. 08:06.250 --> 08:10.390 We are processing order for items. 08:12.910 --> 08:14.950 And we're going to list them. 08:22.030 --> 08:24.670 So maybe this can be a book. 08:24.670 --> 08:31.120 But here we've got an array to be book and movie. 08:31.900 --> 08:35.830 And I said let's have yet another array. 08:36.340 --> 08:39.940 Maybe apple and orange. 08:41.500 --> 08:42.010 Okay. 08:42.010 --> 08:43.690 Let's see if this works. 08:45.460 --> 08:45.760 Okay. 08:45.790 --> 08:47.650 So here are the orders. 08:49.630 --> 08:54.370 So we have just one item and then we've got multiple items. 08:54.370 --> 08:56.200 So everything works fine.