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‫-: Hi.

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‫Within this lecture we are going to create our first project

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‫in order to understand classes a little bit more.

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‫Rather than going with single view app,

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‫this time I'm going to go for Mac OS

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‫and I'm going to create a command line tool.

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‫If you remember, I showed you this technique

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‫in the beginning of this course

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‫before we dive into the playgrounds.

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‫So if you had a problem with playground

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‫there is a high probability that you have worked

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‫with this now, but if you haven't, it's not an issue,

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‫just create a new Mac OS line command tool

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‫and you can name it musician class.

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‫So that's what we are going to build in this lecture.

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‫We're going to create a musician class

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‫and we are going to see almost every aspect

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‫of classes so that we can understand them better

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‫and we can just implement them in our projects as well.

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‫So this is going to run this codes inside of our Mac

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‫and we are not gonna be dealing

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‫with main dot storyboards or simulators.

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‫So if you just run this, it'll print out the result in logs

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‫so we can actually follow and track what's going

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‫on inside of logs as well as you can see it printed out.

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‫Hello world.

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‫Can we do this in playgrounds?

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‫Of course we can, but we are going to learn a lot

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‫and we are going to work

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‫with different kinds of view controllers.

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‫We are going to see how to work

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‫with multiple view controllers

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‫or dot swift files in this case, not view controllers

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‫so that it would make sense to work this inside

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‫of command line tool.

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‫So come over here and just say file new, Okay?

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‫because we are going to add a new file.

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‫So let's say file, okay?

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‫And rather than coco touch class, I'm going to go

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‫for a Swift file because I'm going to create a class

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‫in the Swift while, and I'm going

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‫to name my class musicians. Okay?

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‫So this will be my musician class,

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‫this will be my model actually.

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‫So in order to create a class, it's fairly

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‫easy, you can just write class, okay?

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‫And then we are going to start with

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‫an upper case rather than lower case.

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‫Remember, in classes we use upper case like this musicians.

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‫And then after you can open a curly brace

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‫and it'll close it for you.

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‫This is your class.

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‫Right now, we actually created our class.

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‫So we can have some attributes,

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‫we can have some actions in this class right?

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‫So let's start, what can a musician have?

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‫It can have a name for example.

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‫Okay, I'm gonna initialize this

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‫to be an empty string first.

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‫So later on it'll have an age.

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‫I'm going to say this is zero

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‫and it will have an instrument as well.

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‫So you can make this an empty string too.

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‫So suppose that we will have this musician's class, okay?

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‫And it will have these three attributes.

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‫So how can we create a musician object?

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‫Since now we have our class, it's fairly easy.

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‫We can go to our main dot swift file,

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‫suppose that main dot swift is your view controller

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‫and we have created a musician class, and now

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‫I can create an object out of that musician class in here.

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‫So first musician will be James

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‫and if I write musicians, it should have show up.

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‫Yeah, it sees the musicians, as you can see

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‫if I do a command B, it will build up the project

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‫or it can come over here to product and say build.

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‫So the files will be synchronized

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‫inside of our xcode project.

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‫So if I write

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‫let James or let something else, if I type musicians

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‫as you can see now it sees the musician's class.

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‫So double click on this,

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‫and as you can see

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‫there is a C character on the left hand side.

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‫If you do a string,

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‫this is kind of creating a string object

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‫like I'm creating a musician's object right now.

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‫So if I open parenthesis and close this, it means

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‫that I'm creating this object out of the musician's class.

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‫And right now my object is actually created.

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‫So I managed to create an James instance

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‫of this musician class.

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‫So as you can see, James has the type musicians

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‫and if I say dot, it can see the attributes

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‫like age, instrument, and name.

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‫So these are the attributes that we have given here.

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‫So let me say property or attribute, okay?

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‫So I can just define the age of James here.

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‫So I can say 50 and I can come over here and say

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‫James dot name is James Hatfield.

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‫Okay? And then later on I can define

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‫the instrument as well, so this will be a guitar.

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‫So do this for your own favorite musician

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‫and you will see it will work.

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‫So let's try to print age of James.

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‫Here you go. We now see the 50.

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‫That's cool, right?

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‫We have created a musician model and we have

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‫created an object out of that model

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‫and we can set the attributes right now.

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‫Now suppose that we are getting

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‫this information from internet.

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‫We're downloading from a database

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‫like Firebase, Okay?

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‫So if we work on a model

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‫this would be much more structural than ever before.

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‫So we can actually save all those values

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‫into array, different arrays

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‫and we can try to synchronize these arrays using indexes.

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‫But if we just create a model out of these values

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‫and we can just add those model values to an array

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‫it will be much more structural.

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‫And we're gonna do that in the following lectures.

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‫Don't worry.

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‫Right now, suppose that I didn't define

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‫the values as I did in the James.

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‫So we have those previously defined values, right?

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‫So let me try to print James dot H

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‫without giving the values.

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‫So what will it be?

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‫It will be zero because why?

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‫Because I have initialized this to be zero, right?

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‫And if I do do this print James dot name

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‫it'll be an empty string.

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‫So what's the problem about that?

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‫So maybe I don't want to initialize this.

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‫Maybe I just want to say this will be an integer

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‫or this will be a string because I don't want to

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‫get number zero when I don't give the age value.

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‫Okay? So can I do this?

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‫Yes, of course I can, but it will give me an error.

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‫So as you can see, class musicians has no initializers.

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‫So if I create a property, if I create an attribute

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‫without initializing, I will get an error.

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‫But there is a solution to that problem as well.

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‫We have something called initializer

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‫and maybe you have heard this

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‫as a constructor in other programming languages.

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‫So there is a special function

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‫in this musician class, in all classes actually

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‫it defines what to do when we create this object

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‫when we create an object out of this musicians.

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‫So I can't do the initialization as well to

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‫make this go away.

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‫But if I don't want to do that

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‫if I don't want to initialize this properties

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‫then I have to create an initializer.

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‫So if you write in it, as you can see

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‫this is an initializer declaration

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‫and this is what happens when an object is created

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‫for the first time or second time.

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‫It doesn't matter actually

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‫when you create an object, it will happen.

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‫So what exactly can we do inside of this unit?

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‫We can do anything we want.

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‫It doesn't have to be related with class musicians at all.

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‫So let me do an example so you will understand it better.

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‫So if I initialize this

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‫and this and this last one,

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‫the error will go away, okay?

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‫And I will just print something inside of my init function.

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‫So I can say musician created for example.

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‫So whenever I create an object, it will print this lock.

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‫So let me create this, James.

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‫As you can see, this is only creating the James

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‫and this will only print out the James dot name

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‫but before it prints, it says musician created.

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‫So whenever I create another instance

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‫of this musician class, it'll again print musician created.

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‫So it isn't related with properties or attributes at all.

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‫Of course we gonna make it related.

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‫But let me do this example as well.

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‫So I'm creating another instance from these musicians.

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‫And if I run this you will see there will

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‫be two musician created lock.

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‫So in init you can write what you wanna do when

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‫an object is created.

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‫So this is Initializer, okay?

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‫And again, you may have heard this

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‫as a constructor in other programming languages.

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‫What we actually wanna do in here is to

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‫get some name agent instrument property values

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‫and assign them as our properties, as our attributes.

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‫We are gonna get those values

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‫from the developer in Main dot Swift.

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‫So let's stop here and do that within the next lecture.