1 00:00:01,170 --> 00:00:07,650 All right, let's look at another important concept in the go programming language, and that is channels 2 00:00:07,920 --> 00:00:12,260 and channels are unique to go, or at least as far as I know, I've never seen them anywhere else. 3 00:00:12,690 --> 00:00:16,790 And channels are not that difficult, but they are incredibly useful. 4 00:00:16,830 --> 00:00:22,410 They are a means of sending information from one part of your program to another part of your program 5 00:00:22,650 --> 00:00:23,350 very easily. 6 00:00:23,880 --> 00:00:30,240 So we've so far, we've seen things we're going to have here is an empty package and our empty program. 7 00:00:30,240 --> 00:00:33,930 I have two packages of it saves me the last time I have Helper's, which is empty. 8 00:00:33,930 --> 00:00:37,740 It has nothing and I have my main package, which just has an empty main function. 9 00:00:38,220 --> 00:00:40,310 Now we've seen how to pass things around before. 10 00:00:40,320 --> 00:00:48,870 For example, I can say func print text and it takes a string as an argument and it returns nothing. 11 00:00:49,590 --> 00:00:55,980 And all it does is log the print line and then the string that I've passed it and then I can call that 12 00:00:55,980 --> 00:00:59,520 function from up here so I could say print text. 13 00:01:01,530 --> 00:01:01,980 Hi. 14 00:01:02,910 --> 00:01:08,910 So what I'm doing is passing information from my main function to my print text function, and that's 15 00:01:08,910 --> 00:01:10,210 one way of passing information. 16 00:01:10,710 --> 00:01:13,950 We also saw how you could do it using pointers and I'm not going to go through that again. 17 00:01:13,950 --> 00:01:15,930 You can just watch that lecture again if you wish to. 18 00:01:16,620 --> 00:01:20,730 Well, there's a third way of doing it, and that way is creating a channel. 19 00:01:20,850 --> 00:01:25,800 So I'm going to get rid of this function and I'm going to get rid of this call to that function. 20 00:01:26,670 --> 00:01:31,500 And we're back to an empty manuchehr or main function. 21 00:01:32,370 --> 00:01:37,140 So now I'm going to create a channel and you create channels in a way that's very similar to the way 22 00:01:37,140 --> 00:01:38,700 that we created maps. 23 00:01:38,700 --> 00:01:40,790 He used the make keyword. 24 00:01:41,130 --> 00:01:48,090 So I'll call this and into Champ, it's going to be a channel of its and it is created by saying make 25 00:01:49,050 --> 00:01:50,520 channel it. 26 00:01:51,270 --> 00:01:57,630 And all that says is I'm creating a channel, a place to send information which will be received in 27 00:01:57,630 --> 00:02:02,060 one or more places in my program, and that channel can only hold it. 28 00:02:02,100 --> 00:02:03,210 That's all that it can hold. 29 00:02:03,930 --> 00:02:05,610 So what do I do with that? 30 00:02:05,640 --> 00:02:06,920 Well, it's pretty straightforward. 31 00:02:06,930 --> 00:02:10,080 Let's create another function and I'll do it above the main function. 32 00:02:10,980 --> 00:02:17,850 And that's going to be called func calculate value. 33 00:02:18,960 --> 00:02:28,860 And it's going to take an argument of its channel and it's a type channel of it and it doesn't return 34 00:02:28,860 --> 00:02:29,220 anything. 35 00:02:30,630 --> 00:02:31,530 And what does this do? 36 00:02:31,530 --> 00:02:38,160 Well, in here I want to generate a random number and then I want to do something with that random number. 37 00:02:38,250 --> 00:02:42,970 And just for fun, I'm going to create my random number function over here and my helper function. 38 00:02:43,680 --> 00:02:47,640 So let's create a random number and it's not as easy as you might think. 39 00:02:48,750 --> 00:02:49,920 We can do it like this. 40 00:02:50,070 --> 00:02:58,800 We could say func random number that takes an argument and we want to create a random number from a 41 00:02:58,800 --> 00:03:03,690 pool of some size and that will be an entry and it will return the random number we calculate. 42 00:03:05,730 --> 00:03:07,930 So what do we do? 43 00:03:08,160 --> 00:03:10,890 We can say, first of all, we could say value. 44 00:03:14,390 --> 00:03:18,200 Is assigned and we're going to call a built in package. 45 00:03:18,230 --> 00:03:23,060 OK, we're going to call it built in package from the go language and it is called math. 46 00:03:23,840 --> 00:03:30,730 So we will use Rande and we're going to choose the correct package here. 47 00:03:30,740 --> 00:03:35,990 We want Rande and the function we want is IMT and there it is Matheran. 48 00:03:36,860 --> 00:03:38,900 And it's going to take an argument. 49 00:03:38,900 --> 00:03:41,970 And the argument it has to take is how big is the pool. 50 00:03:42,410 --> 00:03:45,030 So that will be m what we passed as a parameter. 51 00:03:45,620 --> 00:03:49,150 So now we've created around a number and we just want to return that. 52 00:03:49,160 --> 00:03:54,020 That's all that we want to do so we can say return value. 53 00:03:55,010 --> 00:03:57,170 OK, so apparently we've created a random number. 54 00:03:57,330 --> 00:04:03,260 Let's go back to our main program and let's get that random number in our calculate function. 55 00:04:04,400 --> 00:04:12,800 So random number, which is just a variable name, is assigned the value of and I want to call random 56 00:04:13,070 --> 00:04:16,130 number Helper's random number and I want to call it from some pool. 57 00:04:16,550 --> 00:04:23,210 Now, I could put 10 in here if I want to, but I'm going to use a constant const and I'll call it num 58 00:04:23,210 --> 00:04:23,660 pool 59 00:04:26,630 --> 00:04:32,660 and I'll make it equal to ten and then I'll just use that constant down here just because I can. 60 00:04:33,470 --> 00:04:38,130 So that would be no pool and we want to return that. 61 00:04:39,650 --> 00:04:40,550 Do we want to return it? 62 00:04:40,580 --> 00:04:43,450 No, we want to use our channel because what we've passed it is a channel. 63 00:04:44,180 --> 00:04:48,680 So I'm going to now pass that random number that I've just generated into my channel. 64 00:04:48,880 --> 00:04:54,620 And I do that using a very simple syntax int channel the channel name, and I'm going to pass it. 65 00:04:55,820 --> 00:04:56,480 Random number. 66 00:04:57,620 --> 00:05:01,610 OK, so now down here, I've created my main function. 67 00:05:01,610 --> 00:05:09,020 I've created that main channel and I want to close it once this check, once this program or this function 68 00:05:09,020 --> 00:05:10,340 is finished executing. 69 00:05:10,350 --> 00:05:11,630 Now we're in our main function. 70 00:05:11,640 --> 00:05:15,230 So technically I don't have to close it because the program will exit as soon as I'm done. 71 00:05:16,040 --> 00:05:19,100 But it's good to get in the habit of doing this. 72 00:05:19,100 --> 00:05:28,370 Defer clothes and my enchante, now that Dhafir is a word we haven't seen yet, and it's when you're 73 00:05:28,370 --> 00:05:32,300 going to be using regularly in our programming as we go through this course. 74 00:05:32,660 --> 00:05:40,190 And all first says is whatever comes after this keyword, defer, execute that as soon as the current 75 00:05:40,190 --> 00:05:41,450 function is done. 76 00:05:42,320 --> 00:05:48,470 Now that becomes useful because in situations where, for example, I open a file or I open a connection 77 00:05:48,470 --> 00:05:53,720 to the database, I don't want to leave those things open forever because every time you open a file 78 00:05:53,750 --> 00:06:00,440 on your file system, you're using one of a limited number of files that you can have open at the same 79 00:06:00,440 --> 00:06:00,790 time. 80 00:06:00,980 --> 00:06:06,260 And if you leave them all open every time you create a file or open a file for reading, for example, 81 00:06:06,860 --> 00:06:09,730 eventually you're going to run out of handles for the files. 82 00:06:10,220 --> 00:06:12,620 So you want to close them after you open them. 83 00:06:12,620 --> 00:06:14,420 And the same is true of database connections. 84 00:06:14,420 --> 00:06:19,070 You can have a limited number of database connections open at a given time, and when you run out, 85 00:06:19,070 --> 00:06:24,800 bad things happen and closing them after the function is finished, after you're finished using that 86 00:06:24,800 --> 00:06:26,410 function is just good practice. 87 00:06:26,420 --> 00:06:28,240 In fact, it's critical you have to do it. 88 00:06:28,490 --> 00:06:32,720 So here I don't want to have I can again, I can have a limited number of channels open. 89 00:06:32,720 --> 00:06:38,120 It's a big number, but if the program runs for seven months or 12 years or whatever, eventually you're 90 00:06:38,120 --> 00:06:38,920 going to run out of them. 91 00:06:39,410 --> 00:06:40,760 So I close them when I'm done with it. 92 00:06:41,060 --> 00:06:43,990 And here I'm just going to do that because it's good practice. 93 00:06:44,720 --> 00:06:51,590 Now we are going to call our calculate values, but I'm going to do it in a way that you haven't seen 94 00:06:51,590 --> 00:06:55,730 yet, and I'm going to do it by sending it off as a concurrent operation. 95 00:06:55,730 --> 00:06:59,690 I'm going to do it by running this routine in its own go routine. 96 00:06:59,870 --> 00:07:01,010 So it runs. 97 00:07:01,250 --> 00:07:04,970 And the nice thing about this is go routines run at the same time. 98 00:07:04,970 --> 00:07:09,350 So if I need to do a thousand things, I don't have to do them one at a time. 99 00:07:09,350 --> 00:07:12,890 I can fire off a thousand go routines, all of which run at the same time. 100 00:07:13,160 --> 00:07:13,970 Thousands, a big number. 101 00:07:13,970 --> 00:07:20,720 But you get the idea and you do that simply by saying go in front of the call to the function that you 102 00:07:20,720 --> 00:07:21,350 want to call. 103 00:07:21,920 --> 00:07:23,330 And that turns into a go routine. 104 00:07:23,330 --> 00:07:27,940 And I'm going to now call calculate value and I'm going to pass my channel into. 105 00:07:31,210 --> 00:07:37,790 There I have done that and now I need to listen for the response to that channel. 106 00:07:38,110 --> 00:07:44,800 So up here I passed Evalu into the channel down here, I want to get a value from the channel and I 107 00:07:44,800 --> 00:07:45,190 do that. 108 00:07:45,640 --> 00:07:47,200 It's a really straightforward syntax. 109 00:07:47,200 --> 00:07:54,670 I'm going to say my no, whatever it is, I'll just call it num is assigned the value of whatever comes 110 00:07:54,670 --> 00:07:55,720 from enchante. 111 00:07:58,430 --> 00:08:00,860 And then I'll print it out, log print online. 112 00:08:02,910 --> 00:08:06,250 And no, all right, so that should work. 113 00:08:06,630 --> 00:08:08,240 Now let's see what happens when we run this. 114 00:08:08,250 --> 00:08:14,040 I'm going to open my terminal window and I'm going to clear the screen and I'm going to just run the 115 00:08:14,040 --> 00:08:14,460 program. 116 00:08:14,470 --> 00:08:16,320 Go run, Mingo. 117 00:08:18,180 --> 00:08:20,460 I got one out of my pool of ten. 118 00:08:20,550 --> 00:08:21,400 Let's run it again. 119 00:08:21,420 --> 00:08:22,410 Go, run, go. 120 00:08:22,590 --> 00:08:23,210 I got one. 121 00:08:23,820 --> 00:08:24,810 Go, run, go. 122 00:08:25,380 --> 00:08:26,100 I got one. 123 00:08:27,390 --> 00:08:29,220 Which doesn't seem terribly random. 124 00:08:29,550 --> 00:08:30,750 And in fact, it's not. 125 00:08:31,140 --> 00:08:33,000 And it's not for a very simple reason. 126 00:08:33,000 --> 00:08:38,790 It would be random if this program was called would be pseudo random if the program wasn't exciting 127 00:08:38,790 --> 00:08:39,930 every time it was called. 128 00:08:40,770 --> 00:08:47,520 But in my helper's file, if I roll over inten, you actually see a little comment here sitting with 129 00:08:47,520 --> 00:08:49,950 the same value results in the same random sequence. 130 00:08:49,950 --> 00:08:54,060 Each run for different numbers, seed with the different values such as time. 131 00:08:54,420 --> 00:08:58,050 Now Unix and A. which yields a constantly changing number. 132 00:08:58,080 --> 00:08:58,520 Aha. 133 00:08:58,540 --> 00:09:01,170 That's all we have to do to get a random number here. 134 00:09:01,860 --> 00:09:06,060 So I need to see it and I see that by saying rande dot seed. 135 00:09:06,420 --> 00:09:10,290 And what I want to do is exactly what they told me inside of those parameters. 136 00:09:10,290 --> 00:09:18,270 I'll go with time dot now, which is the current time now, which is the current time, and then I want 137 00:09:18,270 --> 00:09:24,050 to get the Unix Nano and that gives me a different number every time I run this. 138 00:09:24,060 --> 00:09:30,930 So if we go back to our main program and we clear the screen and we run it again, this time I got two 139 00:09:30,930 --> 00:09:34,560 and I run it again and this time I got three and this time I get six. 140 00:09:34,560 --> 00:09:36,290 So now it is more random. 141 00:09:36,780 --> 00:09:41,520 So what it's returning is a random number between zero and my number. 142 00:09:41,520 --> 00:09:48,690 So if I make this number pool a thousand and clear the screen and run it again, this time I got 50, 143 00:09:48,990 --> 00:09:52,170 this time I got 412 730. 144 00:09:52,170 --> 00:09:56,040 But the important thing here is not the fact that we're getting random numbers, it's where we're getting 145 00:09:56,040 --> 00:09:56,970 that value from. 146 00:09:56,970 --> 00:09:57,890 So let's go through this. 147 00:09:58,620 --> 00:10:00,090 I have a main package. 148 00:10:00,300 --> 00:10:03,390 I have my main function that runs first. 149 00:10:03,960 --> 00:10:06,630 Actually, it declares this constant first, but this runs first. 150 00:10:07,230 --> 00:10:13,020 And then I create a channel, a channel that can only hold INTs if I try to pass a string or a float 151 00:10:13,020 --> 00:10:14,690 or a date or something else in there. 152 00:10:14,730 --> 00:10:15,540 It's not going to work. 153 00:10:15,800 --> 00:10:17,070 You can't even compile the program. 154 00:10:17,070 --> 00:10:18,080 It can only take it. 155 00:10:18,750 --> 00:10:23,700 Then I say when I'm finished running close this channel, which is good practice, not necessarily in 156 00:10:23,700 --> 00:10:25,680 the main function, but I'm going to do it anyway. 157 00:10:26,070 --> 00:10:31,500 And in later situations where we use this main function to initialize channels and then the main function 158 00:10:31,500 --> 00:10:35,130 continues to run for a long time, that's definitely critical. 159 00:10:35,130 --> 00:10:39,690 So do that get in a good habit of closing things that need to be closed and we'll be going through a 160 00:10:39,690 --> 00:10:41,070 number of things that need to be closed. 161 00:10:42,270 --> 00:10:48,540 So I create the channel, I defer the clothes, and then I say fire off a new go routine, run this 162 00:10:50,310 --> 00:10:54,030 by itself and its own routine and hand it the channel. 163 00:10:54,210 --> 00:10:54,600 Great. 164 00:10:54,600 --> 00:10:58,830 So I then this fires off up here. 165 00:10:59,340 --> 00:11:04,860 This as a go routine and that takes a channel is an argument and I generate a random number and then 166 00:11:04,860 --> 00:11:08,790 I just say, push that back into the channel you've just given me down here. 167 00:11:09,000 --> 00:11:16,380 I'm listening for that channel and when I get a value from it, it's passed into this variable num and 168 00:11:16,380 --> 00:11:17,220 then I just print it out. 169 00:11:17,610 --> 00:11:23,670 So that's just a really useful way of passing information from one package to another package or one 170 00:11:23,670 --> 00:11:26,250 part of your program to another part of your program. 171 00:11:26,430 --> 00:11:32,880 Incredibly powerful and very, very useful when you have more than one package in your program, which 172 00:11:32,880 --> 00:11:33,660 we're going to have. 173 00:11:34,080 --> 00:11:38,370 So those are channels and we'll be using them regularly as time goes on.