WEBVTT 00:00.260 --> 00:06.500 Okay guys, now finally with references let's have an example with loops. 00:08.150 --> 00:12.080 So this would be a for each loop ref. 00:12.080 --> 00:14.090 So let me create such file. 00:14.540 --> 00:18.260 So I just wanted without any preconditions. 00:18.260 --> 00:24.110 Show you an example where we have a large data set generated but a large data set. 00:24.110 --> 00:29.150 And we're going to see how can we access data by reference. 00:29.150 --> 00:34.580 And we're going to see if there was any difference which version was faster. 00:34.580 --> 00:38.810 It might also be useful for you to do such experiments. 00:39.890 --> 00:44.750 So to this large array variable I'm going to assign the result of range function. 00:44.750 --> 00:50.840 So range function allows us to generate a big array with some value. 00:50.870 --> 00:53.000 Let's just use the default one. 00:53.420 --> 00:57.200 And I'd like 1 million elements. 00:57.200 --> 01:05.030 By the way, in PHP you can write numbers like this using underscore just for it to be more visually 01:05.030 --> 01:05.750 readable. 01:05.780 --> 01:09.230 This is still a valid number 1 million. 01:10.160 --> 01:14.240 Now let's see how can we calculate the time of the execution. 01:14.240 --> 01:20.510 So we can use the Microtime function and pass true to it. 01:21.110 --> 01:24.740 So we're gonna get the time at specific points. 01:24.890 --> 01:27.170 So this is before we run the code. 01:27.170 --> 01:30.020 And then we're going to do the same after we run the code. 01:30.020 --> 01:32.780 And we're gonna show the difference. 01:33.710 --> 01:33.950 Okay. 01:33.980 --> 01:36.470 So what are we about to do? 01:36.590 --> 01:43.220 Well I would like to just double every element inside this large array. 01:43.220 --> 01:46.100 Keep in mind it's 1 million elements. 01:46.100 --> 01:48.320 And I just want the result. 01:48.320 --> 01:52.190 So I just want the result to be stored someplace. 01:52.190 --> 01:58.700 So if we use the for each array well we need a kind of an output array. 01:58.790 --> 02:01.250 So let's define the out variable. 02:01.280 --> 02:05.360 and by default this is an empty array. 02:06.170 --> 02:06.500 Okay. 02:06.530 --> 02:16.430 So now we can do for each and go over the large array where every element that we have. 02:16.430 --> 02:19.700 Well we're going to add to the out array. 02:19.730 --> 02:25.190 Now in PHP the simplest way to add a new element is using such syntax. 02:25.220 --> 02:30.800 This essentially means add a new element at the end of this array. 02:31.490 --> 02:36.050 And in this case that's just value times two. 02:36.680 --> 02:43.970 And additionally I think that we can also keep track of the used memory. 02:46.250 --> 02:48.140 And this can also be used. 02:48.140 --> 02:50.630 This can also be done by using function. 02:50.630 --> 02:54.140 This is memory get usage. 02:54.860 --> 03:05.000 And also at the end we can get the end time by just running Microtime with the true parameter and also 03:05.030 --> 03:07.160 the end memory. 03:07.190 --> 03:10.940 Let's get it using memory. 03:13.130 --> 03:15.380 Get usage. 03:16.880 --> 03:17.330 All right. 03:17.330 --> 03:21.110 And now let's output the results. 03:22.850 --> 03:25.520 So first we need to display the time. 03:25.520 --> 03:35.090 And let's concatenate the results of subtracting the end time or subtracting the start time from the 03:35.090 --> 03:36.200 end time. 03:40.610 --> 03:43.340 So this would be in seconds. 03:43.790 --> 03:45.650 That's the first result. 03:46.220 --> 03:50.810 And another result is the memory. 03:51.830 --> 03:55.250 So time and memory. 03:58.010 --> 04:02.520 So here let's round the result using the round function. 04:02.550 --> 04:09.660 Since the result would be in bytes, let's also convert that to megabytes. 04:10.350 --> 04:16.230 So first we do end memory minus start memory. 04:16.260 --> 04:18.690 I think it's called start mem. 04:19.560 --> 04:21.450 Let's rename that to memory. 04:25.950 --> 04:26.820 All right. 04:27.510 --> 04:34.650 And then we divide that by 1024 to convert to kilobytes. 04:34.650 --> 04:39.480 And again 1024 converting to megabytes. 04:39.510 --> 04:48.540 Quick reminder 1024 bytes makes one kilobyte 1024kB makes one megabyte. 04:49.110 --> 04:52.230 Also, let's adjust this to be megabytes. 04:52.230 --> 04:53.460 And now let's run that. 04:53.460 --> 04:56.400 So this is for each dash ref. 04:56.460 --> 04:58.800 And here are the results. 04:58.800 --> 05:01.260 That's the time it took to process the array. 05:01.260 --> 05:03.540 And that was the memory usage. 05:03.570 --> 05:05.580 16MB. 05:05.610 --> 05:09.780 Now let's see, what will we have with the references. 05:09.810 --> 05:14.640 Now keep in mind that here we had to have two arrays. 05:14.640 --> 05:23.160 So the large array and this outer array that just contained the results of those calculations. 05:23.970 --> 05:27.750 Now let's modify this example to use references. 05:27.750 --> 05:34.620 So with loops you can use references by adding the end sign before this variable. 05:34.740 --> 05:42.360 So what this does with the loops is that instead of creating a copy of every element of the array that 05:42.360 --> 05:48.180 we go over, we actually directly reference it. 05:48.210 --> 05:49.500 So now. 05:52.800 --> 06:00.090 If you do something like this, you are just gonna modify an entry inside this original array. 06:00.120 --> 06:07.380 So this means with this example we don't need the out array as we are going to be modifying the original 06:07.380 --> 06:08.040 value. 06:09.480 --> 06:12.360 Okay, so let me run this example. 06:12.360 --> 06:15.030 So let's quickly go over the results. 06:15.090 --> 06:18.030 That's the time without references. 06:18.210 --> 06:21.150 And this is the time with references. 06:21.150 --> 06:23.820 So with references it's slower. 06:23.820 --> 06:25.350 It took more time. 06:25.350 --> 06:29.250 That's the memory without using references in loops. 06:29.310 --> 06:33.270 And that's the memory used with references. 06:33.270 --> 06:36.570 So it's almost double the memory. 06:36.750 --> 06:39.780 That's why I'm saying this. 06:39.780 --> 06:45.090 Be careful if you try to use references for optimizations. 06:45.090 --> 06:53.670 So in this case using reference lets you directly modify the value in the original array, which wouldn't 06:53.670 --> 06:57.390 be possible otherwise with the for each loop. 06:57.390 --> 06:59.310 So that's the use case here. 06:59.340 --> 07:02.820 Not any potential optimizations.