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So let's begin with a gentle introduction to the go programming language, and this might be a refresher



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for somebody that's worked in go a little bit but needs to kind of refresh their memory.



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It might be an introduction to this language for people that are familiar with other languages.



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Or it might be the very first time you've ever written a program of any sort.



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It doesn't matter.



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We're going to go through a series of brief lectures that give us just enough information to begin to



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start with Web applications.



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So you're going to learn the very basics and go and it's not that hard.



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So I'm using visual studio code, which I still don't like and may never like, but I'm going to force



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myself to use it for this portion of the course so that I at least know enough to give people a hand



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if they run into difficulties.



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So I start by starting up visual studio code, which I've done, and I have an empty project.



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So if I come in to hear the Explorer and click on that, it says you have not yet open the folder.



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So it's open a folder.



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I'm going to create a new folder.



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It doesn't matter where I create it.



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Learning go, but remember where you create it in case you need to go find the files, create and then



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I'll go into that folder.



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Open.



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And in here, I'm going to create an empty file of first of all, I'll get rid of this welcome screen



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and then I will create a new file by rolling over the Explorer and hitting this little icon that says



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new file.



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And I'll call this file.



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I mean, I'll go and every go file has to end with Dutko.



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It has to have that extension.



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So I create it.



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Now I have an empty file name Mango.



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And as is the case with all go files, the very first thing that must appear to go file is a declaration



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that says, what package do you belong to?



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And the keyword to make that happen is simply package.



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And it is a convention, I can call this Treva if I wanted to, but it is a convention that your main



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package is called name.



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So I'm going to call my mink's.



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I like to adhere to good standards and write what is known as idiomatic go.



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All right.



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So I've declared this main package and I declare my package is being made.



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Every main package must consist of at least one function.



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And if you don't know what a function is, don't worry, you're going to find out shortly.



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And that function must be called main.



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All right.



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So I can do that.



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How do you declare a function and go with the keyword?



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OK, and this one has to be called main.



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And because it's a function, it has to have parentheses and a function body begins and ends with curly



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braces.



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So what are these parentheses for?



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First of all, functions have to have parentheses because you need sometimes to pass information to



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a function which we're going to do momentarily.



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But the main function doesn't take any parameters at all.



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So technically speaking, this is a good program.



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It has a package named Main.



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It has a main package, in other words, and it has one function in there called Main, but it doesn't



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do anything yet.



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Well, I need to do something.



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What can I do?



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Well, let's let's think about functions for a minute.



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Maybe maybe I can create another function down here called func say say something.



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And that's going to take an argument because I need to know what to say.



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So I'm going to give it an argument.



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And the argument is going to be a string, just a word or a phrase or whatever it's going to be.



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It's going to be something stored a bunch of characters in a string.



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And because it's a string and string starts with the letter S..



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I'll give my variable the rather simple name of S.



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You think that might be enough, but it's not.



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I need to tell this function and the compiler what kind of parameter this is.



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What is is it a number?



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Is it a date.



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Is it a what.



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Is it a string.



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Well, in this case it is a string and string is one of the primitives built in to go.



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So I have a function name say something that takes one argument s which is a string and it's going to



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return some value.



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This is the great thing about functions, the little bits of code you can use over and over and over.



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You can call them from many places in your program or pretty much any place in your program and a lot



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of cases.



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And you can return some value so I can return a string.



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That's what I want to return.



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Now, this is going to be a really stupid function.



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All it's going to do is return whatever it's passed.



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And how do I return something from a function?



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Well, not surprisingly, the word to make that happen, the key word is return.



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And I only have one thing I can possibly return, which is a string s, so I haven't done anything else.



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All right.



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So now I've created a program that has two functions.



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The main function, which is the entry point for the application and func say something.



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Can I run this?



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Let's see what happens.



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So I save it.



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And you notice when I saved it, it applied formatting, which is rather thoughtful.



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How do I run this program?



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Go to terminal new terminal window and I'm going to simply write Go, run, maeng, go.



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So what should happen?



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Well, nothing actually should happen.



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Let's try it.



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Nothing happened.



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Why?



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I'm going to have this function.



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Surely something should take place.



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Well, I've never called this function so I can do that in my main function.



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This is the first bit of code that will get executed in the program.



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No matter how complex this program is.



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This main function is the entry point.



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So I can call that function.



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And I could do that just by saying say something and say something.



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If I just do it like that is going to say, oh, there's an error, you can't go any further.



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Why not?



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Because say something expects to receive a string.



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Well it's just puts a string in there and then go you can write a string by putting quotes around it.



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Hello.



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OK, I wanted to say hello now surely that's going to do something.



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So I've saved my code and I come down here and I'll clear the screen by hitting control and I'll run



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it.



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Well, nothing happened well, nothing happened because I called the function say something which returns



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a type of string, and I didn't do anything with that string.



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I need to store it somewhere.



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I need someplace to hold that value, whatever it returns back.



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And I do that with a variable.



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So let's create our first variable and we're going to create a variable two different ways.



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But this is the first way we're going to do it with the keyword VA.



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VA is a variable and the variable has to have a name.



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And I'll call this what to say.



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Variables can't have spaces in there.



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They can't start with the number.



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Pretty much anything else is good to go.



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But the approach that I'm using here, which is to start with a lowercase letter and then capitalize



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all the other ones cavalcades, that's the convention.



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In some case, you're going to want to start with a capital letter, but we'll get to that when we get



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to that.



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Right now, I've got a variable what to say and it still has an error y because as I said a while ago,



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go is a strictly typed or strongly typed language.



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It has to have a type.



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I'll give this the type string, which is the only type we know about right now.



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So perfect.



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I've created a variable, but I haven't done anything with it.



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And Visual Studio Code has helpfully reminded me that this is a problem.



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I have an error.



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So I see Red underline over here and over here on the right hand side, I see a little red thing in



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the bar that says there's an error in your code right there.



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Well, what is there?



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I can roll the mouse over it and it will tell me what to say declared but not used.



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And this is one of the nice features of go.



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If you create a variable, you have to use it.



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Otherwise the program will refuse to compile and that is a good thing.



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You do not want unused variables floating around your code base doing absolutely nothing, just cluttering



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it and taking up space.



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So I need to use this variable.



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Well, I was a minute ago, I said I need somewhere to hold the value returned by this function.



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This is the perfect place to use it.



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What to say is equal to say something.



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Well, how come I still have an error?



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Because even though I've created this variable, initialized it when I created using the keyword, it's



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just created as an empty string.



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There's nothing in there.



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It's a type string, but it has no characters in there.



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And even though I stored a value in it here, I still haven't done anything with that variable.



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I need to do something.



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So what am I going to do?



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I'm simply going to print it to the terminal.



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How am I going to do that?



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Well, there's a number of ways of doing it in the little hollow world example we had early on in the



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course we use the FMT print line function.



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This time we're going to use a different package that does pretty much the same thing for our purposes



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today.



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Anyway, I'm going to use the log package log, which is a reserved word so I can't have a variable



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name variable named Log.



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It is a package and if I hit DOT Visual Studio Code says, hey, you're using the package log, it has



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all these functions.



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Which ones do you want?



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Well, I'm going to use print line Priam TLM and log print line is a function.



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Therefore it must have parentheses and it expects but does not require.



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In this case, it expects something to be in between those parentheses, the values that I'm passing



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to that particular function print line and what I want to pass it is what to say.



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And if I say this.



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But if I save it after I give the variable to correct and save it, life is good.



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Now, I should be able to run this program.



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So when I come down here, I saved it.



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We're good.



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When I come down here and clear the screen and say, go, run, man, go look at what's going to happen.



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First of all, it's going to say package means so great.



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We're the main package.



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That's the one that has to run first.



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This is my entry point and we're going to use the funk machine, which is the absolute entry point.



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But where did this come from, this import log?



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Well, when I imported when I use the package log, I need to tell my program that I'm using that package.



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I need to import it.



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And once I import it, I have access to all of the functions that are built into that package.



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And as we saw a minute ago, we can look again logged.



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All of these functions are part of that package.



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Therefore, I can use them.



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So some are some are other things.



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But we they're all available to us.



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If I don't import it, I can't use it.



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So this idea, like every good idea out there, integrated development environment, when you use a



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package, it does the imports for you.



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If it's not working for you or you're just using a text editor or whatever you need, you need to manually



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type in import log.



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But we're using visual studio code, so life is good.



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So I go to run this.



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It'll say, where's the main package?



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Here it is.



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Where's the main function?



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Here it is.



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What do you want me to do?



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First of all, you're declaring a variable.



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Perfect.



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I've created a variable.



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It has an empty string now in I want you to store into what to say this variable, whatever the function,



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say something returns so I can say it calls it.



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I passed it.



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Hello.



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Say something.



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What do I do with it?



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I just return whatever you pass me.



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So I'm storing this value in this variable and now I'm printing it out.



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Very good.



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I can use that function again and I can do it this way.



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I can say declare another string variable var say something else.



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And it's also a string of other spills, something right, and then I can just say down here, say something



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else is a sign, the value of say something and I'll pass it goodbye.



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And then I will print that to the terminal because I can't declare this variable even if I store something



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in it, unless I do something with it.



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So log line.



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Say are something else, some.



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What am I doing here?



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Loved up front line, say something else.



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All right, now I want to run it, even though I'm calling the same function, say something, I'm passing



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at a different parameter.



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So I should, first of all, call the function, get the word hello, print it out, call the function



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again, store the variable somewhere else and print that out.



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Let's see if it works.



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Hello, goodbye, and I can even do it this way, logged print line without a variable print line,



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say something finally, it doesn't matter what I put in there, so I save that.



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And now I'm passing a function as a parameter.



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I'm actually passing that call to this function as a parameter to log print line.



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Will that work?



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Yes, it does.



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Perfect.



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All right.



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Last thing I want to do, I want to talk about some different variable types.



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So I'm going to create another variable.



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I'm going to call this are because I want it to be not of type string, but of another primitive type



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it and it just holds whole numbers.



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So down here, after finally I will give a lecture.



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Let's not give it a value.



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Let's see what happens if we leave it on initialized.



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If I say log dot.



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Print line.



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I declared a variable.



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Now I'm using it, but at no point did I give it a value.



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What's it going to print out there?



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That's going to clear the screen.



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Run the program.



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And apparently the value of the type and if you don't give it a value, defaults to zero.



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That makes perfect sense.



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But if I give it a value here, I is equal to seven and save it and clear the screen and run the program



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again.



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Now I have seven.



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What if I give a different value?



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I equals eight.



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Well, it seems useless.



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I assigned the value of seven to I and I immediately assign the value of eight to what does it get.



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Go Roumain go perfect.



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It has eight.



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Last thing I want to talk about just for fun, ok is that functions can actually return more than one



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value and this is unusual.



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You don't see this in a lot of programming languages.



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Java doesn't have it.



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You can do the same thing in by returning an array but go it has first class functions.



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You can return more than one value.



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So let's change our function.



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It's going to return to strings, string string.



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Now, when you have more than one thing being returned, you need to wrap those in parentheses.



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That's it.



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So I want to return a string and a string.



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Now I immediately have an error.



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First of all, say something returns to values and you're only storing it in one.



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So that's bad.



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Here, say something is supposed to return to values, but you're only returning one, so that's bad.



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So we need to fix this.



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So we need to return another value.



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So let's just return hardcoded string world there they are gone.



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But up here I have two errors.



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How am I going to get the two values string string into a on this side of the parentheses?



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Well, as you might expect, the very first thing I'm returning is whatever was passed to me.



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The second thing is the key word is the is the word world, which is just a string.



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So I need somewhere to store that.



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Well, I can do it like this.



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VAR world string.



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OK, and then here I could say I want you to take the second return value and staut and world.



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OK, that works world.



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Rule declared safe.



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So that's gone.



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I'm still not using it and here where I call the function again world.



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Save and down here when I don't need to do anything because I'm not doing anything with the return values,



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but it says you're still not using the word world.



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Well, I don't want that.



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That's a totally unnecessary second parameter.



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And I put it in there purely for illustrative purposes.



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I actually don't even want to use the word world.



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It's just a complete waste of time.



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What I can do instead of storing the value is just tell the compiler, ignore the second return parameter.



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And that's what the underscore character means.



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Ignore the second return parameter.



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That's what the underscore means.



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And now I should be able to, once I save this, come down here, clear the screen and run the program.



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And it should work.



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And it does.



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All right.



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So you might notice that go is rather rather strict other programming languages like P, P or not.



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And I'll give you an example of that.



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So I have running in an idea over here and I've created a new empty file, which I called maned up.



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And if you don't know or don't care about it, just ignore this.



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But all files have to start with that little token.



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With a question mark on the pointy bracket and variables and start with the dollar sign for reasons



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I'll never understand, but they do so I can call this s four string is given the value of hello.



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That's no problem.



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It works.



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And then I'm down here, I can say Echo Dollar Sign s to print that to the screen.



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So now when I run this run maned not run meaned up, it runs prints out the word hello perfect.



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But I can now do this dollar sign as is equal to seven.



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I can store an intern there and the program will run just fine.



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No problem.



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It prints out seven and I can to create and create another variable.



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VAR two is given the value of zero and even though I'm not using it, we will run.



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And there's a reason for that is an interpreted language, which means any time you run a file on the



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same is true of Python, for example, or JavaScript.



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It has to be run through an interpreter and an interpreter takes that file, loads it from disk, loads



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it into memory, passes through it, runs it through the interpreter, produces machine code and then



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executes the instructions, which means by default, interpreting languages are pretty slow, in contrast.



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Go is a strongly typed, compiled language, which means we don't actually ever serve or do anything



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with mango, all of our go files and by the time we're done, this course will have many go files in



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different packages.



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Even they're compiled into a single program, a binary.



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And that binary is executed and it is much, much faster.



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And because it's compiled, go has the ability to say, well, you're not using that that variable.



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I'm not going to let you do that.



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In contrast, over IP, we can do this.



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We can have variables that change type because it's not strongly typed.



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We can also have variables that are never used because we need to load it into disk and execute it through



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the interpreter before we can actually do anything with it.



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So it's possible to have sloppy code go more or less forces you to be concise and only to include things



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you're actually using.



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So the other advantage, of course, is a compiled language is much, much faster than an interpreted



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language.



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Go is, on average, more than two hundred times faster than a similar function executed in say so it



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has that going for and it forces me to keep my code clean, which makes me rather happy.



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All right.



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That's enough for this time around.



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In the next lecture, we will begin to look at structure and types in defining our own variable types.



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And we'll also look at a few more primitives along the way.



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So far, we've only seen string and we also have time.



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The time type, we have float's.



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We have other primitives.



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You should be familiar with those and you will be by the time we get through this little introduction



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refresher.



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See you in the next lecture.