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So or come back in this class and begin to talk about a very important topic of reference counting reference

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counting is essentially vaid that you assign your memories and how you decide whether a new value of

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your property is going to have its own memory space or whether it is going to point to another memory

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as ways and how often they do get are located and how often they get released.

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Now the first counting is specifically in Objective-C is not the easiest thing to teach and to learn

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but there are some very good practices that simplify this for us in this case and I will go through

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almost all of the reference counting strategies that are out there and I will try to come up with some

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of the easiest ones for you so you can use them something you want to keep in mind is that you probably

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are not going to use any of these for a very very long time for the most part you can actually stick

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with the default ways of doing things and nothing is going to go wrong.

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But then the time will come that you are doing something a little bit more complicated and you have

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objects that they have internal references to each other and then you need to know how to deal with

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those.

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So with that in mind the squarehead into Estcourt and in code I'm going to start a new app command line

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tool Objective-C.

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I'm going to call it R R.

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And Orkus stands for automatic reference counting that's like the closest thing you can find in our

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X code for garbage collection for finding what object is no more in use and has to be released and what

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objects they have to stay in their stack because somebody is still accessing them.

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Well I'll call this one Aurukun.

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Let's say read or read right.

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Because that's the first thing that they want to talk about and of course these Objective-C

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then the yeah I'm going to go ahead and say I have a class interface let's call it my class.

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It has a superclass of this object.

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And then of course I need to have my implementation of my class and in my implementation I have nothing.

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Because simply just want introduce some properties as property envenomed.

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I'm going to make it like this and when I say it is atomic it is also read write and it is also strong.

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And I'm going to call this one the full string.

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So what does it mean.

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This is the default behavior of Objective-C.

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It means when you define any variables by default they get to become atomic read right and strong.

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So theoretically writing this line and writing this one are exactly the same thing.

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It would automatically would have those qualifiers added to it.

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I'm going to call this one or fall the string.

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So that's the easiest thing.

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So we got that out of the way.

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Now what is difficult or not difficult but what we need to discuss is so what all these things you know

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what do we do with them and how do we use them.

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Let's go ahead and get started.

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The most basic one which is this one reads right.

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I'm going to say I have a property and that property has only one qualifier hard to read right and then

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I have the same thing.

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Once again this is called My read write a string.

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So this is a read write to string and then I have another one which is read only a string.

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And I'm sure you can imagine what happens now if I go ahead and make two of these properties in my file.

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Anyway I am I'm going to say my class my object is my class knew that I could go ahead and say my object

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got read right becomes hello but if I try the same thing we might read only

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look what happens.

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It gives me an error saying that hey you cannot set anything to a read only property simply because

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the only properties are meant to be only changed as an initialization level.

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So for that you cannot change anything.

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So because of that behavior we can only set the read only by using an EVA.

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And that means using the set to read only a string which is something that we often do when we want

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to do some internal calculations.

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So more of this will come in in a few minutes and we're talking about eyeballs.

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But for now let's say that for most everything you probably want to use or read write which is a part

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of the default behavior.

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So let's keep that in mind and let's move on to another example which we're going to talk about atomicity

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of a variable.

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So for doing that I'm actually going to go ahead and start a new project let me copy everything from

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here because you're going to need a lot of these things.

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And when I go in here and say command line tool are you putting more.

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Tomas the object is c and then in this one I'm going to paste everything.

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So here on the top forget the default ones if you know what they are.

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You could add everything in the same project.

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For me I'm trying to have everything in one screen.

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That's why I like it this way.

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So the laugh then becomes atomic.

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One of them becomes none atomic.

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And if you remember atomic is the default behavior.

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And of course I'm going to change names to atomic string and non atomic string.

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So let's see what these two things are.

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I'm only going to write two keywords for each of these in the hopes that you know that would kind of

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explain it for what's coming up.

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Atomic is multithreaded and lock non-atomic is single threaded and unlock.

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Let's see what all these things mean.

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Thomas It essentially is about the way that something gets access.

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Imagine if you have two different threads or three different threads are trying to change a value of

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something.

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Maybe you have a thread that is you or you are reading you are seeing things and then you have another

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thread which is trying to kind of cure back and then read some information.

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I you have another thread that you are doing some calculations.

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So it's very common to have multiple threads at all times.

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So in a situation where all these threads are trying to access the same value it becomes a little bit

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unclear of which one is accessing it first which is writing it first.

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And when we are trying to read it tonight which of the values we get access to now in a situation where

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you have a variable which is atomic.

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It means every thread can simultaneously access it.

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It means every thread before the access that they will lock its value.

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So in the meantime while doing something on it if you try to access not one you see the previous value

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which is a good thing.

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It means you will get some value back your value will not be needed because that trade is doing something

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that is the downside of it is you might not get the correct value.

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It might be that you're getting the value right before an operation and you're not seeing what is happening

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inside the operation.

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Now in a non-atomic value Well what's happening is is only one thread that can access the value at any

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given time and it doesn't try to lock it.

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It just goes on and it starts changing the values of that viable.

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And the downside of it is obviously you might get a near lvalue.

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So let's see this in practice.

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And I should warn you that some of the gold I'm going to write in here is a little bit at last for us.

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We're going to see these in in a few sections when we talk about trading sessions.

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But for now we kind of need to just just see them as a demonstration.

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Don't worry about specific ways that they work.

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So here I have my object and I have my object dot atomic string and I'm going write most of them in

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one line saying is my non atomic a string.

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And they both have a let's say a default value.

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So by now we have an object that both of these things are set to something and we know if we print these

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are we're going to see essentially the same thing.

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So this next thing is going to be quite new for us and that is how to start a new thread.

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So solving it two ideas usually are an operation that happens by something else you know when you access

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to a network or you might want to manually you know write thread to update your you I but here when

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I started that word on my own I'm going to say dispatch in a dispatch from say dispatch a sink dispatch

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a sink and the one I want to use is this.

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CH This gets main gets global Q And then for the identifier I want to use that dispatch you are priority

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bygones.

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No flags.

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Here is the body of the code.

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So this piece of code essentially is going and starting in thread for us and then I start this new thread

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I'm going to do this.

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I'm going to save both of these values.

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Let's give them something else let's call it the second value.

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So that is Sanken value.

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And then I'm going to go ahead I start another thread in here and say both of them they get it here

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at the rally.

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So what's happening.

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We have a default value that is our clients value.

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Two other threads are accessing these values and changing them to other things and they're all happening

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simultaneously at the background level.

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So the very important question becomes so what is the value in either of these two right now.

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So if I go in here and I say a slide and I would say are atomic is.

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I would say my object not atomic is string.

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And I would copy that and say non atomic is not atomic a string.

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We should see what's there is not sought here.

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If I run this it shows up.

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Now here we see that atomic kids are still defiant.

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So atomic is reading the value that was there.

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Those other two threads haven't managed to change it.

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Non-atomic is the second value.

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So if I go ahead and say well let's go to one of these threads and change their priority.

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You say high priority.

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I run this one now my non atomic value reflects the most recent update.

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It is as you know a single threaded.

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It's not locked.

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It goes and says well finished this thread finished that thread finished that thread and then give me

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the value.

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One of my atomic s thing says well I'm just trying to get you the result and the result I can find the

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right of way is whatever it was there.

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I'm not going to worry about those other threats.

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So there is some advantages to using either of the two and the situation will come for you when you

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know that you have to use non-atomic.

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But for most everything you can use atomic which is the default behavior in X code anyway.

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So that was about the atrocities of a value bet.

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Now let's move on to another topic and that's another off whether an object is being copied or it is

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being assigned.

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So we'll see what that means in a Cygan like the last time I'm actually going to copy everything from

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here and then I start a new project this new project I'm going to call it to argue copy versus assign

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Objective-C of course.

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And bear with me as I paced this and I change a lot of stuff.

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So off the top I don't have to worry about the atomic part anymore.

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I'm going to change one of them to copy quali copied the string and then I'm going to change one of

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them to sign and I'm going to call this one.

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I signed this thing and then it changed that effect.

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And in here I don't have any of those threading and whatnot but I do have is that they both have one

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initial value let's call it copy the string is assigned a string.

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I don't want them boys to be looking at the same static value I wanted it to be actually inside another

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variable.

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So I'm going to go ahead and say how I in this mutable string and when I call it a value which is an

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S mutable a string string by a string and the other string says default.

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So the reason I want it to be inside an estimate of a string is because I want to change that value

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really soon.

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So I'm going to say most of these guys they are value so whether they are copied or assigned for that

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is copy or assign they are going to be the same value of a value which is on an estimate about a string

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for the next piece is actually very easy once there are those assigned to one I'm going to go ahead

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and say Well Van has actually had some stuff at hand and some new things.

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So as you can all imagine right now the value inside the value is the default space.

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And some new things.

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Now what happens if we print or copy this thing and assign the string.

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So I'm going to say copy it.

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Copy the string I signed and signed is going to be signed the string.

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Let's run this project I execute that you should see down there my so that copy is a default.

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It doesn't have those extra bits of text and a sign is having everything.

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So this is what it means.

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It means that copy any value but of the type copy.

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When ever you assign them whenever you initialize them they make their own copy of the value and they

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place it in a newer spot in the memory while a sign essentially keeps a pointer to that part to whatever

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was of value in there just so that you know we know a sign is very similar to the page and copy is very

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similar if you are strong and that's something we're going to see in the next example.

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What is the difference between these two guys.

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So to demonstrate the relationship between a strong and Veeck qualifiers I'm actually going to go ahead

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and start a new project and this one I'm actually doing it in suites simply because that's something

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that we use more often in swift.

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I'm going to say are strong.

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We are stryfe in here.

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Here's what we're going to do.

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I won't write an app that has a very basic user commenting relationship.

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So here go ahead and say on the very top I have a class called common.

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Then you have another one class.

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This one is users.

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So we have two classes so far they have common and we have usage so for comment I have about our text

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which is going to be empty at the beginning so that's it takes the body off the comment.

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I also have a use for it.

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I have a that I'm going to call it on there and that's going to be a user.

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And that's essentially who has written that comment.

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Now for a user itself every user has a name which by default is empathy.

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And then every user also has a Carman's

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Harmons which is going to be our comments of course.

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Now you know in real life scenarios this obviously would be an array of comments.

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But for now I'm trying to simplify things and I'm assuming one user can comment on what other user and

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vice versa.

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Nobody can comment on multiple different people.

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So that's that and of course I need to have an initialiser in it here.

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Can to say in name.

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And I think that's pretty much all I would need because come on they have to just start a new one.

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So that's easy I'm going to go ahead and say self-taught name becomes input's name and I'm going to

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say self-taught Carmens becomes a new comer.

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So so far we have two classes that each of them deals with something one of them deals with having writing

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comments.

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The other one deals with holding onto all of our users.

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Now the tricky thing here is the balls have a variable of each others type within them and that's somehow

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a common situation.

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You know you're right you're a staff innovator.

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They have data relationship between them and we have to find a way to make sure that our retained count

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doesn't go up beyond what's meant to be.

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So here's how they're going to test this whole thing.

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I'm going to go ahead and say let's make one use of let's say my user that's going to be a user of.

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And the only thing I have to give it is John.

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Right.

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So I have a user with the name John.

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And then I'm going to go ahead and preens how many retain count I have for this user.

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So I'm going to go ahead and save print in my print.

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I'm going to go ahead and say our users count is what is it.

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Is this something that you know is perhaps new for you and that is get retain count.

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So I'm going to say see I get to retain count.

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And what I want to get the count of.

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I want to get the count of discard.

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So what it does it gets how many copies of these are in the memory.

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And by default this should be torn out because it should be one for the actual valuable and one for

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the hour.

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So let's run this

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and once or up front it says the user's account is true.

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So that's so far perfectly working the way we expected it.

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Now what happens when I do this when I say my use of dot comments which is that valuable in here.

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Dot on there which is this you in here becomes my user.

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So sure I think you could have a lot of situations where a user has commented on themselves or tool

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users or to use as they have commented on each other and each of them is being used both as the guy

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who owns the comment as well as the guy who writes that comment.

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So now my user comment owner has become my user.

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And now let's go ahead and reprint this user accounts.

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Now is

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trick.

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And here's the problem.

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The problem is that the next time we were trying to point to this user through this comment on our not

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only we pointed out that but also he copied it in a newer space in our memory which is really not a

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good thing.

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We ended up having more than one copy of my user and that's being assigned for only this one.

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So to remedy that I'm going to go ahead and say that it's a very simple fix.

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This on average which is only going to be a point there has to be a weak link.

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If it is a weakling it's means like a sign don't copy it means do not copy the value.

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So let's go ahead and say it and now both counts are still too simply because here be are setting that

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we are not adding another account

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and finally in this lesson we're going to talk about uveitis or directly accessing valuables.

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Let's see what they are.

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I'm going to start a new project in export objective c and this is going to be.

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It has our eyes objective see.

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Let's see what they mean.

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Imagine we have a class up here I have an interface interface Let's call this a user class and as object

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as you know we don't know if you need anything else for it.

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I also have implementation and that's going to be a user.

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And then I have some functions in here and I'm going to call this one some function doesn't matter what

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it does some function.

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Now if you remember whenever you had a situation like this and you had a property that property and

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that property was friends and as a string to some property we could do two different things when we

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wanted to access that property.

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You could either say on this or some property that becomes hello and all of it would say self that some

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property and that becomes held.

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So what's the difference between these two.

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I'm actually going to write it V-twin here within the actual body of it.

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This here says directly accessing the value of that.

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And this one says accessing very well Rudy said.

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So what is the difference between these two things.

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When you declare a property using the property in Objective-C it automatically does something that we

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call synthesize and what synthesize does is essentially sets the two variables sit there and get there.

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So what you don't know is by default this thing now has something called Set some property is actually

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a function called void set.

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Some property is already being built which receives a property and sets that.

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And if you use this dot operation you're essentially accessing that method.

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If you use the underscore one you access the variable directly.

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So in most cases that doesn't really make a difference for you.

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You could use either or simply because you don't care about what is within the body of the set.

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But if you want it you could manually do the sender.

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So go ahead add in your value.

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I'm going to call it manual property for my money or property I'm going to write a boast that said there

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and they get there myself I'm going to go ahead and say void them.

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And here is the set mining all property to something and then I'm going to go ahead and say and that's

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a strange because it is of the type of string right manual property return.

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What should it return it should return the cell the manual property.

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So here is how I have essentially written Boerse of these manuals.

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And in this set we should receive an input value that you can call it nine you want to recalculate new

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value and then it of course has to have the same self that non-null property has to become new value

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or.

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And this is the only time that this happens or you might not want to do that or you might want to do

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something before you sign for whatever reason you might have a situation that you need to do something

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before you sign it.

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So that's essentially how these two will be different.

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You could get used to using either of them.

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I personally for the most part I use this system accessing through the other simply because of this

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very fact if I decide to change something in there I can easily go ahead and do it and if I had so many

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of these being applied like that I can always just change something in the solder.

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And they've all will be affected by it.

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Well if I use the IRA if I use the direct taxes then I have to go to each of them and manually change

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that value.

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So that's about that are AMANDO a quick recap of everything that we did because it's kind of a lot of

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stuff in this one lesson.

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So here we did these things we talked about atomic on non-atomic.

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If you remember this was a single trial that might be nil.

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This one was multithread that never Nan might be wrong though it might show you the wrong value.

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We talked about a sign on copy and we said in the sign of point a location in memory coffee or Surely

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I typed that the wrong points copy essentially copies information for itself.

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That's about that which is a weak link.

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Existing as long as someone has connections to it are the strong is a strong link living for as long

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as the cycle lives.

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These warnings aren't exactly right that for instance would be kids essentially saying maintain it as

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long as someone else has a strong relationship to it.

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What I'm trying to I don't know in my own way I'm trying to simplify things a little bit.

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So that's about that different qualifiers for properties.

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For the most part we stick to strong.

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And if you're so go read the right of your so go for it.

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But there might be situations that you decide to change any of these.

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Like I said you can live with the default values for now and when the time comes.

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Hopefully by then you will know yourself if you have a change of those with that in mind on this very

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long lesson finished let's move on to our next lesson.