WEBVTT 00:01.040 --> 00:09.380 Higher order functions are functions that either take functions as arguments or return functions. 00:09.380 --> 00:18.380 In this case, apply is a higher order function because, as you may be noticed or not, this OP argument 00:18.380 --> 00:24.650 is then called as a function which makes apply the higher order function. 00:25.400 --> 00:34.010 So we can also add an arrow function like this and pass it to the call when we are calling apply, which 00:34.010 --> 00:37.550 makes apply the higher order function. 00:41.000 --> 00:42.740 Let's see another example. 00:42.740 --> 00:45.380 So consider that we have this array. 00:45.380 --> 00:48.410 We would like to sort the people by age. 00:49.220 --> 00:52.640 We can use use sort for that passing this array. 00:52.790 --> 00:59.930 And the second argument in this case is just an arrow function that is doing the sorting logic. 00:59.930 --> 01:05.420 That's why you sought is an higher order function. 01:05.960 --> 01:11.450 So function that either takes functions as arguments or returns a function. 01:11.450 --> 01:14.000 And that's the result in this case. 01:15.620 --> 01:19.550 So we've already covered higher order functions before. 01:19.700 --> 01:27.200 If I now search for the Arraymap function inside the project, I can find it in the arrow functions 01:27.200 --> 01:30.170 and the anonymous functions files. 01:30.800 --> 01:38.120 So actually we've been using higher order functions without knowing that they are higher order functions. 01:38.150 --> 01:40.430 So Arraymap is a good example. 01:40.430 --> 01:46.670 And a lot of array related functions are also higher order functions. 01:46.670 --> 01:52.340 So I don't think there is a point in rewriting the examples from the slides. 01:52.370 --> 01:56.930 Instead, let's create a higher order function that returns a function. 01:58.010 --> 02:01.400 So let's create a higher Order. 02:01.880 --> 02:04.460 FBX file for this example. 02:05.090 --> 02:12.890 PHP tag and let me put some data because I just don't want to waste your time typing this on the video. 02:13.250 --> 02:20.360 So what I'd like to do with this array, this multi-dimensional array is from this main array, I only 02:20.360 --> 02:26.240 want the elements that are under the key role will have an admin. 02:26.240 --> 02:30.380 So at least that's the first filter that I would like to create. 02:30.380 --> 02:37.250 But I would like to be also a little bit more flexible with what filters I can create. 02:37.250 --> 02:43.970 So I'm not gonna make a specific function that will perform the array filtering for that key. 02:44.120 --> 02:49.070 We're going to create a generic higher order function that we can then reuse. 02:49.070 --> 02:52.970 However we want to filter for different properties. 02:53.870 --> 02:59.000 So I'm creating a function I'm going to call it create filter. 02:59.000 --> 03:07.370 And what it needs to know is which key I'm interested in and what needs to be value of that key. 03:10.790 --> 03:18.140 So that's not a higher order function yet, but now it is because I am returning a function from it. 03:18.890 --> 03:28.760 So this function for every item that it receives, it just needs to compare the item key with value. 03:28.790 --> 03:31.310 That's a strict equality operator. 03:31.340 --> 03:33.770 Now this might look complex. 03:33.770 --> 03:38.900 Right now you might not understand what the hell I'm doing, but don't worry about that. 03:38.930 --> 03:42.890 We're gonna run this function and I'm gonna explain it. 03:42.920 --> 03:50.480 So first, since this is a higher order function which returns a new function, this means we first 03:50.480 --> 03:55.910 need to call it with some parameters to get a function that only then we can use. 03:55.910 --> 03:58.460 So that's the purpose here. 03:58.490 --> 04:02.780 So I am creating a function that I'm going gonna call is admin. 04:02.780 --> 04:06.380 Remember, functions are first class citizens in PHP. 04:06.410 --> 04:11.720 They can be passed around as arguments, returned from functions, or assigned to variables. 04:11.720 --> 04:13.190 That's why I can do that. 04:13.220 --> 04:19.370 Now I'm calling create filter and take a look at the arguments that we have. 04:19.400 --> 04:21.320 We've got the key and value. 04:21.350 --> 04:24.110 Now those are the keys. 04:26.120 --> 04:31.250 So I'd like the role key to be exactly an admin. 04:31.250 --> 04:35.780 So I am creating a filtering function that does exactly this. 04:35.810 --> 04:37.400 What I'm gonna do with it. 04:37.430 --> 04:43.310 Well I'm gonna get the admins using the built in PHP array filter. 04:43.310 --> 04:44.270 By the way. 04:44.300 --> 04:53.840 There's also a higher order function, because one of the arguments here is a function, our filtering 04:53.840 --> 04:54.800 function. 04:54.800 --> 05:02.970 So the way it works is that for every element from the past array which is users this main array. 05:04.620 --> 05:07.920 Every item will be passed to this function. 05:07.920 --> 05:10.650 So how does our function look like? 05:10.650 --> 05:14.280 Well, we've created it using this higher order function. 05:14.370 --> 05:17.760 And it's gonna receive an item. 05:17.760 --> 05:22.980 That's why when we refer to item key we actually refer. 05:23.100 --> 05:25.590 This is for example an item. 05:25.950 --> 05:29.940 And in this item that's a key and value. 05:29.940 --> 05:32.670 Well that's this part. 05:33.870 --> 05:38.640 So we should be getting only the users that are admins. 05:38.640 --> 05:41.130 Let me squeeze that more into the screen. 05:41.130 --> 05:43.770 So it's visible what's happening. 05:43.800 --> 05:46.770 So finally I need to run that. 05:46.800 --> 05:52.200 So let's do Vardump and let's just see who's the admin. 05:52.590 --> 05:57.090 Let's open the terminal and run higher order PHP. 05:57.300 --> 06:04.250 And the result is an array with only one item because only Alice is an admin. 06:05.060 --> 06:06.050 I think that's correct. 06:06.080 --> 06:07.760 Others are users. 06:10.310 --> 06:15.710 Now we can create another example I can make another function called is Bob. 06:15.740 --> 06:21.590 If for any reason I'd like to talk to everyone who's name is Bob. 06:24.890 --> 06:27.830 So the name has to be Bob. 06:31.940 --> 06:37.490 And I can just directly vardump that without using any additional variables. 06:37.970 --> 06:44.960 So I do array filter on users and calling the is Bob function in this case. 06:46.370 --> 06:47.510 Now let's run that. 06:47.510 --> 06:58.370 And I expect in this second result to get one element inside this array which should match our requirements. 06:58.370 --> 07:00.560 So the name should be Bob.