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So will come back again in this lesson and we going to talk about class extensions and what a class

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extension is is essentially exactly the same thing as a category you know Objective C but for swift.

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So if you use classic stations to add new features to existing classes or the classes that we don't

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have access to all the classic stations to add new features to our own classes simply for the purpose

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of marginalizing our code.

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So in this season I'm going to show you how to use glass extensions which is going to be rather simple

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and then I'm going to show you a picture essentially of an app that I'm developing myself and you can

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see how widely I'm using extensions just so that you know I make sure that my code is simple and readable

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and my colleagues who are working with me on the app or so easily understand my process.

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So go ahead and do it.

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And I'm going to start a new project this time a command line for swift and I'm going to call it class

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extensions.

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And then in here cause extensions are very very simple.

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Here is what we do.

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I'm going to go ahead and say I have a class on that class I'm going to call it my class doesn't have

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a superclass or does have superclass.

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It doesn't not function do something.

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And that's again very simple something you have seen many many times.

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It has a function that does something and then I'm going to go ahead and say extension and this extension

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is for my class on my extension has a function let's call it.

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Do I not think so.

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That's about that.

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I have a clause on that clause has an extension and if I go ahead and say let's use this by saying that

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my object is my class.

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So I made an object of that class and I can simply go ahead and say my object d'art.

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Now we have access to both of these functions the function from the actual cause of the function from

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the extension class and that's about that that's how you do extensions.

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You're right extension the name of your class and then you are.

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It is as if you're inside the body of that class and you are writing your stuff whichever way you like

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it to be.

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One thing that you have to keep in mind is that you can do something like this for instance the channel

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say I have a string between the body of the extension.

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These kind of things the stored properties you must have them in the original class dictionary.

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So you have to actually do it here.

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Primarily we use or at least I use class extensions for situations when I want to do functions if I

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want to add extra functions there and particularly for when I want to do something called a class function.

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That's something I want to show you in the next lesson up.

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This error obviously you know what's happening is that this object isn't explicitly arms wrapped optional.

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I'm saying well you need an initialization.

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I'm going to say if this was the case just to silence that error I'm going to say you with a default

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value.

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So that is extension.

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Now let's go ahead then use extensions on an existing class something that is needed.

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Right.

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So I'm going to go and I don't say remove all of these say extension strings.

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So I want to add a new feature or a new function with string class.

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And the thing I want to add is this.

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What we did before which was numbers only.

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So it's going to be much easier put in the lesson that we delta-V textfield delegates here and in here

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I had this function and then copy all of these.

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Of course we have to change some of it but there's a matter I'm going to bring it to my new extension

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on say that is a function and this function is called numbers only.

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And what is it going to do what is going to return as Thring which is only the numbers of that that

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the input value.

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So I'm going to go in here say that numbers is that remove characters that is purrfect separated them

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terrified.

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Let's join.

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Blah blah that's perfect.

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So what I want to do is this.

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And the ending here.

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I want to say to return what do I want in return.

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I want return the joined version.

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So I want to get the characters in something and then that thing I want to make sure that they return

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the one that only has numbers.

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Now what is that thing that they want to get from that is itself.

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Because self is this a string.

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So I'm going to get this stuff from self bracket's the sky.

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There's set everything that is not and numbers and then add them to each other and then return that

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one.

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So now I have this function let me get rid the all the comments it's easy and I can you know zoom into

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the whole thing easier on that I'm gonna go ahead and say I have variable mightest are which is the

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type of string and it is actually this that I've got.

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There's a lot of numbers of random characters.

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I'm going to save prints numbers only.

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Is what is that that is going to be.

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Boy I need a semicolon.

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I'm typing back and forth between Objective-C and sweet and this is going to be my s are I've got.

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What is it on numbers only.

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So I can actually go ahead and say hey get my string reaches a string and apply a function called numbers

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only.

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And this function only works here because I have the extension for a string in here.

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You fit on this.

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Now we should be able to see exactly what we expected to see

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say numbers only is these parts are we shouldn't have any way of making short of it both is five for

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eight Yes nine eight and for six.

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And then at the end it got to 500 on 60.

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Perfect.

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So that is how you got extensions.

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Extensions are very very common.

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Like I promised I'm going to show you one app of mine.

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Here's the OP you're kind of halfway through.

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As you can imagine that is so much is still happening.

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And we haven't finished a lot of the different things in here.

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But as you can see every class is broken into so many many extensions simply because I want my code

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to be easier and easy easily readable for my colleagues on you know anyone else who might be accessing

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these.

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So for instance if I go through a cloud that reads single Whatever is all the code that there is in

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this one fine.

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This is all the code that is in here.

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This is all the code that is in here.

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It makes things a lot easier for me.

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Let me show you another one that kind of you know perhaps makes easier sense and a simpler one here

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for instance I have a property view controller that is you know a view controller like the ones we have

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seen in the past.

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And then my property viewpoint you to has something that at some borders it has something that adds

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that content to.

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It has something to do with the map.

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It has something to do with the labels in it.

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But each of them has its own extension simply because by having the extensions I make sure that my code

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is far more modularized and it's also a lot easier for everybody else to read it.

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If I tell a colleague of mine that there seems to be an issue with the map in the proper The View Controller

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they know they have to immediately coming here and they work on this one file which really makes our

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lives a lot easier.

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Specifically when we were working together on larger projects we did see these in the future as well

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when we work on version control on how you have to you know essentially go with the best the strategies

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of making sure that you and other people can work easily with each other.

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So with that in mind let's move on to our next lesson.

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This was extensions and I'll see you in the next line.