1 00:00:01,230 --> 00:00:07,470 OK, so I'm still in our main Dongo, but I've deleted everything except what you see on the screen 2 00:00:07,470 --> 00:00:12,840 here, I just have a package declaration and empty brain function and I've left say something that function 3 00:00:12,840 --> 00:00:13,830 we created alone. 4 00:00:14,130 --> 00:00:18,720 And I want to talk about eventually I'm going to get to type's instructs, but I want to talk about 5 00:00:18,720 --> 00:00:21,170 variables and functions just a little bit more. 6 00:00:21,600 --> 00:00:27,780 And I want to draw your attention to new ways to initialize variables and alternate ways to initialize 7 00:00:27,780 --> 00:00:31,480 variables that are similar to the one we saw last time around. 8 00:00:31,800 --> 00:00:34,260 So in my main function, I have nothing. 9 00:00:34,260 --> 00:00:39,210 And above that I'm going to declare a variable outside of the main function, which will give me an 10 00:00:39,210 --> 00:00:42,530 opportunity to talk about scope and variable shadowing. 11 00:00:43,350 --> 00:00:46,860 So I'm going to create a variable var s string. 12 00:00:47,110 --> 00:00:49,770 OK, that's one way to declare a variable. 13 00:00:49,770 --> 00:00:50,640 That's what we did before. 14 00:00:50,670 --> 00:00:54,030 There's another way to do it, to declare it and initialize it at the same time. 15 00:00:54,030 --> 00:00:56,280 And I'll call this seven. 16 00:00:56,700 --> 00:01:03,180 So I've declared a variable of type S that the go compiler is smart enough to say I'm going to infer 17 00:01:03,180 --> 00:01:05,550 the type based upon what you're setting it equal to. 18 00:01:05,580 --> 00:01:08,190 This is a string, therefore X is now a string. 19 00:01:08,580 --> 00:01:18,090 And in my main function, the very first thing I'm going to do is say log print line and I will print 20 00:01:18,090 --> 00:01:19,140 that variable X. 21 00:01:19,590 --> 00:01:24,410 So this variable is declared outside of this function. 22 00:01:24,750 --> 00:01:29,430 Therefore this variable is available to every function in this package. 23 00:01:29,550 --> 00:01:32,420 OK, so that is the scope of this variable. 24 00:01:32,430 --> 00:01:38,670 When I declare a variable in here, var that's two equals six. 25 00:01:39,930 --> 00:01:42,800 This is only available inside the main function. 26 00:01:42,810 --> 00:01:46,890 Say something, doesn't know anything about it, but you notice something here that's a bit of a problem. 27 00:01:46,920 --> 00:01:50,070 OK, well maybe don't, let's just give it an example. 28 00:01:50,070 --> 00:01:52,890 So I print out just to make this work. 29 00:01:52,890 --> 00:01:55,260 Let's get rid of have this log print line s. 30 00:01:55,530 --> 00:02:01,440 Let's duplicate that line log print line S. 31 00:02:01,680 --> 00:02:04,950 S two is comma and then two. 32 00:02:06,840 --> 00:02:14,640 And here I'll put S is and then s now you notice here that I've passed two strings to this one that 33 00:02:14,640 --> 00:02:19,560 I've written by hand by putting quotes around it and one that is a variable and I've done the same thing 34 00:02:19,560 --> 00:02:19,800 here. 35 00:02:19,800 --> 00:02:23,880 Logged up print line is what's called a very ADIC function that will be seeing a little bit later on. 36 00:02:24,150 --> 00:02:28,350 It means you can take one or more parameters or even know parameters. 37 00:02:28,380 --> 00:02:34,200 OK, so all this is going to have all this going to happen right now is I'm going to run the main program. 38 00:02:34,290 --> 00:02:36,090 I'm going to say go run bingo. 39 00:02:36,390 --> 00:02:43,620 And it will run this program and say in the main function, assign a sign, the value of six, the characters 40 00:02:43,620 --> 00:02:50,160 six to the string variable to then print whatever the value of S's and print whatever the value of S2 41 00:02:50,160 --> 00:02:50,370 is. 42 00:02:50,400 --> 00:02:51,040 Let's run that. 43 00:02:51,630 --> 00:02:55,650 So let me say this and go run mango. 44 00:02:57,260 --> 00:03:04,530 Seven to six, perfect, that's exactly what I expected to happen, but now let's add a call to this 45 00:03:04,530 --> 00:03:05,430 function down here. 46 00:03:05,430 --> 00:03:11,300 Say something, say something, and I'm going to pass it x, x, x, OK? 47 00:03:11,340 --> 00:03:13,620 Just because I know that's very different than anything I have so far. 48 00:03:13,650 --> 00:03:14,710 So what do you think is going to happen? 49 00:03:15,270 --> 00:03:17,670 I'm going to come down here and say, say something. 50 00:03:18,060 --> 00:03:20,790 And it takes a parameter called s. 51 00:03:21,090 --> 00:03:25,860 I already have an S up here and it's set the value of seven and I have an S down here. 52 00:03:26,160 --> 00:03:28,080 Which s does this refer to. 53 00:03:28,080 --> 00:03:30,720 Does it refer to this s or this. 54 00:03:30,720 --> 00:03:36,990 S It's not clear and that's a clear example of why you need to be careful with your variable names. 55 00:03:37,030 --> 00:03:38,310 Let's run it and see what happens. 56 00:03:40,500 --> 00:03:51,330 So it says, don't forget to print that out log print line tests, and in front of that, I'll put S 57 00:03:51,570 --> 00:03:55,830 from the say something. 58 00:03:58,370 --> 00:04:02,910 Funk, is this safe that cleared the screen? 59 00:04:02,930 --> 00:04:03,560 Run it again. 60 00:04:03,590 --> 00:04:09,010 Let's find out which s that actually is s from the say something funky is X, X, X. 61 00:04:09,380 --> 00:04:17,300 So here you have this variable s, which you might think is this value from up here being overwritten 62 00:04:17,300 --> 00:04:23,270 because we used a the same variable name for the parameter and we can fix that just by saying as three. 63 00:04:24,910 --> 00:04:30,940 And we run out of turns three and now it's run it, so save that and see what happens. 64 00:04:32,260 --> 00:04:34,090 Clear the screen, go run Mingo. 65 00:04:34,120 --> 00:04:35,020 What should happen? 66 00:04:35,530 --> 00:04:42,040 Well, it should say, first of all, print s, which we know is a package level variable with a value 67 00:04:42,040 --> 00:04:48,940 of seven spelled out print s to which I assigned to value to right here so that you print out six spelled 68 00:04:48,940 --> 00:04:56,680 out then I pass x x x to say something which calls that variable s three which should, what should 69 00:04:56,680 --> 00:05:01,990 happen here is it should say s from the say something func is s from up here seven. 70 00:05:01,990 --> 00:05:03,790 So I should see seven, six, seven. 71 00:05:04,450 --> 00:05:04,990 Let's run it. 72 00:05:05,860 --> 00:05:07,640 Seven, six, seven. 73 00:05:07,750 --> 00:05:08,380 Perfect. 74 00:05:08,680 --> 00:05:09,920 That's ideal. 75 00:05:10,540 --> 00:05:14,250 All right, so there's one example of of things you need to pay attention to. 76 00:05:14,260 --> 00:05:16,630 There are other ways that variable shadowing can happen. 77 00:05:16,900 --> 00:05:23,560 I might, for example, come up in the main function, declare a new variable called s using a different 78 00:05:23,560 --> 00:05:24,060 syntax. 79 00:05:24,070 --> 00:05:26,590 So far all we've seen is this vast string. 80 00:05:27,100 --> 00:05:27,790 And I can do that. 81 00:05:28,000 --> 00:05:29,530 Absolutely, I can do that. 82 00:05:29,890 --> 00:05:35,860 But as far as this function is concerned, s every time I refer to it is going to be whatever of value 83 00:05:35,860 --> 00:05:37,180 I give it within this function. 84 00:05:37,180 --> 00:05:39,000 It's never going to pay attention to this one. 85 00:05:39,610 --> 00:05:44,080 So instead, let's let's look at a different way of initializing a variable S. 86 00:05:45,100 --> 00:05:47,640 S and now I'm not going to use the equals sign. 87 00:05:47,650 --> 00:05:51,970 I'm going to use the column equal sine and I'm going to give that the value of eight. 88 00:05:53,350 --> 00:05:56,050 Eventually I'm going to get confused as to which numbers I'm using. 89 00:05:56,050 --> 00:05:58,410 But as long as I keep it to five or less, I should be OK. 90 00:05:58,690 --> 00:06:00,810 So I've created a new variable here in a different way. 91 00:06:00,820 --> 00:06:05,830 And again, this is because the compiler is very smart, because I didn't use an equal sign. 92 00:06:06,370 --> 00:06:11,620 Actually, what it's doing is saying take this variable, whatever, whatever it is, give it the type 93 00:06:11,620 --> 00:06:12,880 of whatever is over here. 94 00:06:12,880 --> 00:06:13,590 That's a string. 95 00:06:14,020 --> 00:06:18,670 So now I have two variables, again, with the same name and it's easy to get confused. 96 00:06:18,850 --> 00:06:23,470 And when you're writing code, you might think when you use the letter s that you're referring to this, 97 00:06:23,770 --> 00:06:25,780 but in fact, you're referring to this. 98 00:06:25,780 --> 00:06:26,590 So don't do that. 99 00:06:26,620 --> 00:06:28,630 Be very careful with your variable names. 100 00:06:28,660 --> 00:06:30,940 OK, but that's one way of getting it. 101 00:06:31,300 --> 00:06:31,750 All right. 102 00:06:31,870 --> 00:06:33,510 Let's move on to a new topic. 103 00:06:34,090 --> 00:06:38,530 Sometimes the primitive variables are not enough to do what you want them to do. 104 00:06:39,130 --> 00:06:46,270 So, for example, let's say that I am thinking about putting a person in a database and there are certain 105 00:06:46,270 --> 00:06:48,430 kinds of information I want to save about that person. 106 00:06:48,760 --> 00:06:54,220 So I want to say first name, last name, phone number, address, whatever it may be, there might 107 00:06:54,220 --> 00:06:58,570 be 30 different things I'm going to store about a particular individual, but I store them in a database. 108 00:06:59,110 --> 00:07:11,350 Now, I could do that if I wanted to by saying via first name string var last name string ver phone 109 00:07:11,350 --> 00:07:18,310 number string var age int there birth date. 110 00:07:18,820 --> 00:07:21,010 And here's a new type that you're not familiar with yet. 111 00:07:21,010 --> 00:07:24,850 But I, I want, I want to store a date, I could store a string, but that's really not a I mean a 112 00:07:24,850 --> 00:07:25,570 string is a string. 113 00:07:25,570 --> 00:07:31,930 It can be anything I want to take advantage of goes strong typing and ensure that when I saw a date 114 00:07:32,050 --> 00:07:35,950 I'm actually storing a date so I could use a built in package. 115 00:07:35,950 --> 00:07:38,590 That's part of the gold standard library called Time. 116 00:07:39,190 --> 00:07:42,130 And the time type I want to store is actually time. 117 00:07:42,670 --> 00:07:46,600 And in that I can store actually a time or a date or a date in a time. 118 00:07:47,020 --> 00:07:47,980 So I'm going to use that. 119 00:07:47,980 --> 00:07:50,230 I could do that and say, OK, there it is. 120 00:07:50,500 --> 00:07:55,750 And every time I wanted to do something with a person, I could pass along one, two, three, four, 121 00:07:55,750 --> 00:07:57,460 five parameters in functions. 122 00:07:57,800 --> 00:08:02,860 What if that gets to twenty function twenty, twenty bits of information I want to pass along. 123 00:08:02,860 --> 00:08:08,560 Suddenly I have functions with twenty parameters that's going to take forever to type it out and it's 124 00:08:08,560 --> 00:08:12,460 going to look ugly on the screen and you'll be scroll scrolling left and right and it gets extremely 125 00:08:12,460 --> 00:08:13,030 confusing. 126 00:08:13,210 --> 00:08:15,730 So we don't do it that way and go. 127 00:08:15,730 --> 00:08:23,260 What we do instead is we define a type and I can call that type user and it is a struct which you may 128 00:08:23,260 --> 00:08:26,530 never have seen before unless you've programmed in C or a similar language. 129 00:08:27,070 --> 00:08:30,850 But a struct is, as its name implies, just a structure. 130 00:08:31,030 --> 00:08:38,740 And I'm defining that by putting curly braces here and saying this struct contains all kinds of bits 131 00:08:38,740 --> 00:08:39,490 of information. 132 00:08:39,790 --> 00:08:47,500 And those are going to be I'm going to call it first name, which is a string last name, which is a 133 00:08:47,500 --> 00:08:47,950 string. 134 00:08:50,290 --> 00:08:55,360 Phone number, which is a string, and I'll tell you why I'm capitalizing that in a moment, but let 135 00:08:55,360 --> 00:09:01,420 me finish typing first age, which is an entry and birth date, which is time. 136 00:09:01,660 --> 00:09:02,080 Time. 137 00:09:04,760 --> 00:09:09,070 And when I say this, it formatted nicely and I can get rid of this, I don't need that. 138 00:09:09,080 --> 00:09:17,450 Instead, instead of having one, two, three, four, five variables, I have one type of variable. 139 00:09:17,480 --> 00:09:18,550 This is not a variable. 140 00:09:18,590 --> 00:09:21,470 This is a type which can be used as a variable. 141 00:09:21,860 --> 00:09:24,230 So let's get rid of this stuff because we don't need it right now. 142 00:09:25,100 --> 00:09:26,240 And let's get rid of this. 143 00:09:27,170 --> 00:09:29,330 Let's get rid of this function altogether, OK? 144 00:09:30,080 --> 00:09:31,100 And save this. 145 00:09:31,490 --> 00:09:33,800 And now I have a main program that does nothing. 146 00:09:33,800 --> 00:09:34,810 I actually don't need that either. 147 00:09:34,820 --> 00:09:35,420 Let me get rid of it. 148 00:09:37,190 --> 00:09:39,710 So I have a main program that does nothing. 149 00:09:39,710 --> 00:09:44,060 I have imported time because I'm using in this struct, but I'm not doing anything yet. 150 00:09:44,090 --> 00:09:47,090 I have this this type defined, but I'm not even using it. 151 00:09:47,600 --> 00:09:49,430 Let me create a user. 152 00:09:49,670 --> 00:09:56,060 So I'm going to do that in my main function by specifying a variable name user and I'm going to use 153 00:09:56,060 --> 00:09:59,690 the shorthand is equal to what is it equal to. 154 00:09:59,900 --> 00:10:07,700 It is equal to a user, which is this one, and it has certain bits of information and the informations 155 00:10:07,700 --> 00:10:18,620 are first name, which I'm going to give the value of Trever and then a comma, last name and a colon 156 00:10:19,070 --> 00:10:21,680 solla and that's enough. 157 00:10:21,680 --> 00:10:23,190 I'm not going to bother populating the rest of it. 158 00:10:23,210 --> 00:10:26,000 The point is, I can specify all of those now. 159 00:10:26,000 --> 00:10:28,310 I've not actually done anything with that variable. 160 00:10:28,310 --> 00:10:32,390 So again, the compiler saying how you declared a variable, but you're not doing anything with it. 161 00:10:32,390 --> 00:10:33,260 That's bad. 162 00:10:34,040 --> 00:10:39,710 And you notice all I did was say this user is of type user with a capital you up here. 163 00:10:40,100 --> 00:10:43,370 And it has these two things filled out, a first name and last name. 164 00:10:43,370 --> 00:10:45,020 I didn't bother filling out the rest of them. 165 00:10:45,020 --> 00:10:46,640 I can, but I'm not going to right now. 166 00:10:47,270 --> 00:10:49,800 How do I access information from that user? 167 00:10:49,820 --> 00:10:51,470 Well, let's use our log function again. 168 00:10:51,770 --> 00:10:54,050 Log print line. 169 00:10:55,220 --> 00:10:56,090 And I'm in that. 170 00:10:56,090 --> 00:11:01,640 I'm going to print user dot first name and that's how I refer to it. 171 00:11:02,000 --> 00:11:06,380 This user has a member or a field called First Name. 172 00:11:06,380 --> 00:11:07,270 I'm going to print that out. 173 00:11:07,490 --> 00:11:13,930 Let's run this, save it, open our terminal and run it and see what happens. 174 00:11:14,030 --> 00:11:15,920 Go run, Mingo. 175 00:11:17,060 --> 00:11:18,290 And it prints up my first name. 176 00:11:18,770 --> 00:11:25,130 What I can also come in here and say print at the last name to use your last name, save it. 177 00:11:25,610 --> 00:11:26,480 Cleared the screen. 178 00:11:26,990 --> 00:11:27,380 Run it. 179 00:11:28,290 --> 00:11:31,790 OK, well what happens if I try to print my birthdate, which I didn't specify. 180 00:11:32,780 --> 00:11:33,560 Let's try that. 181 00:11:36,890 --> 00:11:44,180 I'll put the birth date just for a label, comma, user, the birth date. 182 00:11:44,840 --> 00:11:46,690 Save it and run it. 183 00:11:47,840 --> 00:11:52,790 And as you might expect, because we didn't initialize birth date up here, we didn't give it a value 184 00:11:52,790 --> 00:11:53,200 here. 185 00:11:54,260 --> 00:11:58,400 It actually prints out the year one January the 1st midnight. 186 00:11:58,430 --> 00:11:58,820 All right. 187 00:11:58,820 --> 00:12:04,360 Well, that that actually is pretty straightforward and it's a really useful way to group things together. 188 00:12:04,400 --> 00:12:13,640 So I did also mention to you that I would tell you why I actually put let me say this, why I put these 189 00:12:14,480 --> 00:12:15,680 things with capital letters. 190 00:12:15,980 --> 00:12:23,360 I put them with capital letters because I knew I might need this user type to be available to another 191 00:12:23,360 --> 00:12:23,900 package. 192 00:12:24,320 --> 00:12:27,410 And go is not an object oriented programming language. 193 00:12:27,410 --> 00:12:34,250 If you're familiar with with objects dealing or object oriented languages like Java or Kotlin or to 194 00:12:34,250 --> 00:12:39,140 a certain extent, then you know what you can do in an object oriented language. 195 00:12:39,140 --> 00:12:48,890 You can say here is a function like I do a new function down here, func, whatever, and it doesn't 196 00:12:48,890 --> 00:12:50,240 do anything and I'm not going to fill it out. 197 00:12:50,690 --> 00:12:53,300 I can make this public, private or protect it. 198 00:12:53,300 --> 00:12:54,140 If it's public. 199 00:12:54,350 --> 00:13:02,150 I can refer to that function from outside of the current package in Java, for example, or if it's 200 00:13:02,600 --> 00:13:06,500 a private, you can't even see it outside of that package. 201 00:13:06,500 --> 00:13:11,000 So it's a way to keep bits of your program that you don't want exposed to other parts of your program 202 00:13:11,120 --> 00:13:12,050 to keep that private. 203 00:13:12,050 --> 00:13:15,440 Wigo doesn't have that functionality using object oriented syntax. 204 00:13:15,440 --> 00:13:22,100 Instead, if I declare a front like this, it's only available within this package, my main package. 205 00:13:22,370 --> 00:13:26,900 But if I declare it like this with a capital letter, it's visible outside of that package. 206 00:13:26,900 --> 00:13:31,640 And you can see that by looking at I see that in practice with another package, by looking at the long 207 00:13:31,650 --> 00:13:38,240 package, notice that every single thing here or every single variable here, you know that this one 208 00:13:38,240 --> 00:13:47,750 is a function fatele f it's visible and it starts with a capital letter in the same way this L date, 209 00:13:47,960 --> 00:13:53,150 which is the name of an int, it actually is visible as well, and it starts with a capital letter. 210 00:13:54,410 --> 00:14:05,540 If I have a variable declared in this package, if I put for example, var special string, that's a 211 00:14:05,540 --> 00:14:09,650 private variable only available to this particular package mean. 212 00:14:09,950 --> 00:14:15,290 But if I gave it a capital letter and this isn't true for the main package, but if you have a capital 213 00:14:15,290 --> 00:14:19,490 letter for the name of a variable inside a package, it's visible outside of that package. 214 00:14:20,060 --> 00:14:20,390 All right. 215 00:14:20,390 --> 00:14:22,790 That's why I put things the way that I did. 216 00:14:23,540 --> 00:14:25,760 So I get rid of these functions. 217 00:14:25,760 --> 00:14:26,510 I'm not using it. 218 00:14:28,130 --> 00:14:32,090 I've got a user type that has members and I now have access to them. 219 00:14:32,090 --> 00:14:39,860 If I want to give more information to this, I can simply say the phone number and it's a string so 220 00:14:39,860 --> 00:14:47,750 I could put one, whatever it is, five five five five five five, one, two and two. 221 00:14:48,290 --> 00:14:49,370 There's my phone number now. 222 00:14:49,370 --> 00:14:50,510 I've populated that. 223 00:14:51,590 --> 00:14:52,730 I do have an error here. 224 00:14:54,750 --> 00:14:56,430 You need to end this with a comma. 225 00:14:58,150 --> 00:15:05,920 So that is type that is variable shadowing life seems to be good so far in the next lecture, we're 226 00:15:05,920 --> 00:15:10,960 going to move on and we'll start looking at other data structures, maps and slices in particular.