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In business and we'll be talking about closures on completion blocks closures closures a very powerful

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feature of excoriation Schrift and we use a similar thing in Objective C called a block.

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And what they do for us is closures are like a function without a name.

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And they help us in situations such as when you want to pass a function as an argument inside another

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function that being used in so many different places the school head into its quote and I'm going to

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start a new project.

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My course command line tool.

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And I'm going to call this one armed soldiers safe and let me maximize profit.

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OK.

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So here the first thing they're going to do is just to get a sense of how you declare and you closure.

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Imagine if you had a function call.

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This is a function doesn't take any arguments and doesn't have any return types.

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So this is the simplest way we could introduce a function his name nor are humans nor return types on

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this the body of our function.

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If I wanted to convert the same thing into a closure I would go ahead and say variable This is closure

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and that closure would become something like this.

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You open the curly brackets first then you talk about your arguments and then you talk about what ever

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that's going to happen between that body.

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So that's what it means.

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It essentially means I have a closure that takes some time.

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Humans are a retentions or something.

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As long as something else is valid as long as the are thing that you want is being met.

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Now this might seem a little bit complicated.

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So let's go ahead and actually write one that helps us doing something.

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I'm going to go ahead and say well how the value of the sets say hi closure to survival is going to

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say high.

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And then I'm going to open Carol-Lee markets.

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I'm going to say my argument is him name which is of the tie the strange.

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And then for that I wanted written another string in the return.

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What would you like to be with.

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I like to say hi.

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And then whatever valuable I have interests.

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So you're articulate this is the function that has an input argument and unharness a string out on returns

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that if I wanted to convert that function in to hear if I wanted to say Fine say hi function I would

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be Diest I would be in name just like what we have done many many times.

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It returns a string and then it does this return date.

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So these two are essentially identical.

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Now I don't want to use the function I want to use the closure now.

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So in the closure I'm going to say I have this and the way I could use it I would save preens.

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What you want to print.

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Here is the value I want to print.

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This closure.

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So I'm going to get the closure of say hi closure for a value such as my name because obviously it receives

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one argument.

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So if Iran does not it should say hi and the name that comes off that in this case we want the space.

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Let's see if that is the case.

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Ari So so far I've managed to have a closure.

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That's the most basic closure that takes in an argument and does something and be understood kind of

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the format of it is whenever you want to have a closure you have this format curly brackets humans returns

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in.

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Now let's go ahead and write another one.

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So in this new one I'm willing to see some of the actual power of closures.

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I'm going to go ahead and actually I'm going to comment everything out in here so that you know they

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don't they don't get mixed down there and I'm printing values.

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And here's a little bit of an explanation of what I'm trying to do.

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Let's say I have a function on my function.

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You don't need to do this because I'm going to change real soon or my function is set my function and

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it has an argument as an as an entry to it.

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Let's say that argument is numbers all right all values song going to save values right and those values

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are an array of integers and then I'm going to do something on these array of values of whatever that

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thing is maybe I want to find out which of those are larger than a hundred so larger than 100.

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And then I want to have another function that goes ahead and says Well tell me the ones that are on

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this farm what I call fun the ones that are smaller than 100 and you can imagine this thing can continue

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for ever so many different functions each of them has a different let's call it condition.

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So here's the thing I have so many functions that are very similar.

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But each time the condition changes.

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So what I'm trying to do is I'm trying to add the condition as one of the arguments in here so I can

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only have one function that can do so many different things and we can do that using Crozier's.

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Let's see how I'm going to manage that when I say give me a function Let's call this one multi multi

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purpose function multi per function like a cat on my multi-port function has these things.

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First of all it has a set of values that receive.

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So let's call it the vowels.

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And the vase is going to be an array of integers.

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So that's the integer values that we want to do something on them.

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But what we want to do and then I'm going to make it a closure.

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I'm going to say it's a closure.

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And that's just the name of a of a closure name of an argument you can call it whatever you like make

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sense to call that closure here.

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I'm going to say it's a closure that receives is an integer and returns a boolean.

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So let's see what that means.

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It means you will have a set of values and you will have another function as an entry for this function.

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I'm going to rewrite this once you are done as if it were two separate functions and you would see how

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it works.

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But for now I'm going to go ahead and say well here's what I want to do.

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I want to say for each number in vowels.

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This is what you want to do.

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You want to say effect closure of that number of each number.

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If that was a valid value I don't know just printed form to say print each name.

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That's all you're going to do for me right now.

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I could change the print to interpret it properly like.

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So what is the condition.

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What is it going to do.

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I know that the numbers might be I don't know 1 2 5 and 5 million 6 million whatever the numbers but

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what is the condition that is going to say if that was true do it.

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That's something that we can do on the fly as he called the function.

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Just go ahead and do it.

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And when I say multifunction moral purpose function which is here that numbers I'm going to give with

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an array of let's say 100 200.

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Seven hundred to twenty five and then the closure is going to say integer in some sort of condition

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and I'm going to say call this integer value and then say the condition is this As long as Val is below

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300.

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So as you can see I called a function with an argument.

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Another argument that that other argument of mine is actually a condition itself.

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So let's run this and see what we get if you Ronit below 300.

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We should get a few of these numbers 100 or 200 225 but maybe one or two.

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So either with a different condition I wanted to see a valid larger or equal to 200.

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Let's see what we get now.

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We should get only the 700 number.

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Now if I were to rewrite this whole thing using nested functions it would be something like this.

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And I really suggest you don't try this with me just just have a look at it because you're not going

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to really use it.

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It would be called a nested function a minus that would receive these values as our input arguments

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and then it would have a body which inside its body it would have another function called our internal

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function that my internal function receives of one value just like here it would receive one integer

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value and would give me back a boolean.

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And then what does it that that one do.

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One says for instance if one is in this case a smaller larger than 100 if it is larger than three hundred

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then return true.

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Right.

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So I may write this a little bit.

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I don't really like typing code like this but sometimes because I'm trying to zoom into the screen for

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you guys I have two.

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So one is if that is that and otherwise else and in the else I'm going to say here it's false.

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So there's an internal function that receives a number it is larger than something it returns true otherwise

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it is false.

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Now within the actual body of function it would say for each value you mean vows.

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Do this what should you do.

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You should say if the internal function of each vial was true then do what we did before.

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Preens this not so in our purines each.

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So this would be the longer we're on if I can show you both of them at the same time.

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So yes this would be a longer way around a nested set of functions and this would be an easier way around

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using a closure that a closure on the fly.

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Whenever I'm calling it I can actually decide what do you want to see.

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Also here I have only one condition but here I could actually decide about the condition as I go through.

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Like I could have this function and I would have another one say multi-purpose function the values or

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another set of values and that other set of values.

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The closure for it says for any value if Val is smaller than 500 so the same function is being used

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at the same time with no changes to the body of the function because in here with no changes to its

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body but is doing two different things for us which obviously is a lot simpler than writing nested functions.

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Some remove that nested function and well remove that.

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And now let's move on to another thing about closures which is called Escaping closures.

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So let's see what is an escaping closure escaping closure escaping closures or a particular type of

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closures that they get called within the arguments of a function and then they can return back from

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the function.

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They are primarily used for synchronous processes asynchronous process is essentially a process where

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you're reading something off the network and it has two word power of your are there threats out there.

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You say user interface thread or computation thread simply because when you make a connection with the

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network backend it might take a little while before you get some results.

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Let's say it takes half a second or one seconds or even you know if you're on a slow connection it might

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take two seconds.

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So in that time your app should unfreeze.

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So they have to work synchronously.

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They have to work parler each other.

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And that's you know what we do for situations like that we use a closure that waits for something and

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then gets essentially popped back.

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So with that in mind let's see how we're going to write an escaping closure and it going here and get

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us.

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We have a function that is going to read the photos from our backend.

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So I'm going to say function the search for talks.

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So this is a function that's going to fetch pictures for us from some sort of a back end that we will

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see in quite a few sections from now to be honest.

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But we can see the process of a closure in here.

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So I'm going to say my fecche photos has a link that is going to be a string that will read and refine

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it and then we want to have a closure for it.

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My closure I'm going to call it completion which is a very common naming convention people code completion.

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Troy prope tells them they completed or not.

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And I'm going to say my completion has these things has a boolean and has a set A and array of a string

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of the names of the photos that it's found.

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It doesn't return anything essentially.

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So I have a completion closure that returns whether it succeeds or not based on that returns a set of

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photos or not.

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And this may have made it optional because it's possible that this bullion is false and we have actually

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failed in fetching information and as a result these things are nil.

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There is nothing in them.

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And then I'm going to go ahead and say well this completion is actually escaping us.

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K ping.

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So it's an escaping closure which will be called later on.

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So similar to the other closures that we had a closure inside the body of the function.

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It gets called immediately but it doesn't get returned immediately on live here.

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That whatever is happening in the van and the bully and or whatever this statement is it must be returned

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right then and escaping closure essentially wait for it to be completed and then it gets returned.

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And that's essentially the power of it.

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So let's see how are we going to use that.

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So here I'm going to go ahead and say let's say we have a status.

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This is not this is far from us from the network status coming from the network.

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So now that we don't have access to a real network I'm going to essentially fake that value.

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I'm going to say let her status and I want to make her status to be something that is either true or

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it is false.

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So I'm going to say Give me an arc for random human or random off to reach this number is either one

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or zero simply because a random number below two is either 0 or 1.

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And I'm going to say if it is status it means if this was true.

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Right.

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If it's not those who want to do something I shouldn't have written it like that and else we should

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do something else.

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So let's see what we have to do.

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Let me get myself better spaces in here.

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So in the case of else that's quite clear.

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We have to say completion.

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We have to say completion false and we didn't get any images.

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That's exactly what he's expecting us to tell him.

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A boolean value and an array of strings which is optional.

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And then in case it was true I'm going to say completion.

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True.

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Yes it succeeded.

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And give us some we know of fake photos for it or one photo or two.

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So that's what we have in here.

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Let me read for my things a little bit again because I need to see everything once again.

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So now we have both of these statuses happening and we have our function.

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Let's go ahead and actually use it.

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I'm going to go ahead and say fecche photos.

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I said give me a link.

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So I'm going to say fake.

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Imagine that was an actual link and then it says what you want to get at the completion of the completion

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I want to get the result I want to get our photos Araik.

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Let's call it now.

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Here is what we do we say if the Rez if resulta was true it means after this event happened that that

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is the very long event that we currently don't have access to.

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But if that one happened and it was successful we got back all of these and if we had a successful result

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then use the photos Araik otherwise or tell us that oh there was an error.

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So on accident.

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Right.

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The other advisors say us do this Corinne's prints error in reading metaphor or something to that effect.

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Now obviously right now I'm faking Duvalier's I can't really be sure what happens but you could try

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it.

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Let me let me go ahead and comment these guys out as well.

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So I only have to deal with this one escaping closures for a Synchronoss tasks.

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So if you run this now depending on whether that number becomes true or false you either get to see

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the photos or we get like here error in reading networth because something happened so we couldn't get

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to the results by so that's about that closures escaping closures closures we use them as a way of passing

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functions as an argument into another function to avoid having nested functions something I personally

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do when you don't really have to do it.

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What they really really like it is I don't put my closures within the body of the argument or actually

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write them as a separate thing.

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So I essentially say type alias under Type early is that they want to call it.

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In this case on line closures or anything that you want to call it.

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And that becomes the entire Declaration of my closure.

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So it says on line closure is that so on and so forth.

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And then in my function I have a link of the type of string and I have a compilation of that type on

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line closure which is also escaping in the form of that little bit so it's easier to see.

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So essentially you managed to put my on line closure inside a separate variable.

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Like I said you didn't see this as a very common practice.

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I really like it this way simply because I end up using the same closure in so many different places

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I might be dealing with it uploading either no photos downloading photos or a lot of times your closure

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is just a bully and that says video or something completed or not.

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So I know that I'm using that to one closure everywhere.

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And if I want to modify they only modify it once so that's about that.

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We looked at different types of closures are simple closures just how they correlate to a function.

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We looked at how to write a function that receives multiple different you know conditions as a closure

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as one of its arguments.

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And each time it can give us a different result.

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And finally we look now at escaping closures and that's about that.

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