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Hey everybody this is Caillat with slopes Loeb's dot com and welcome back to the Eric swift course in

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this section we're going to talk about subjects now subjects are a special form of observable.

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There observables but they have a special function special ability each one is a little bit different

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from the other.

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Of course just like always you can subscribe and dynamically add elements to subjects just like you

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can with observables.

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Now there are currently four kinds of subjects in ARC Swift.

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We're only going to be talking about three of them but they're pretty cool.

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So we're going to talk about publish subjects in this video and then in the next video we'll talk about

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behavior subjects and after behavior subjects we're going to talk about variables and you're probably

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thinking wait variables that's a normal part of swift.

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You're right.

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But a variable in our swift is a little bit different.

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So we're going to begin by talking about published subjects so go ahead and pull open your artics playground

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go ahead and right click on one of the playground pages and click.

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New playground page.

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We're going to call this publish subject.

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And let's go ahead and select all and delete it.

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Of course we need to import our acts Swift.

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We need to import playground support and we need to call playground page.

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Current DOT needs indefinite.

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In definite execution and set that to be equal to true.

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After that we're going to go ahead and create our very first publish subject.

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So go ahead and type var publish subject whip's publish subject and set it to be equal to type published

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subject.

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Now something you need to know is when you create a published subject you need to give it an explicit

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type.

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So we're gonna give it an explicit type of string and we're going to instantiate it by using two parentheses.

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Now what we can do with a publish subject is we can add values to it.

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Check it out.

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If I call publish subject make sure that you select the one with the lowercase p.

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And if I call dot on next I can pass in an element of string.

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So for instance I could say hello and now I have added an element to my published subject.

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Now you probably notice why isn't it doing anything.

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We haven't subscribed yet so let's go ahead and let's create a subscription.

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So go ahead and type let pub sub subscription and we're going to set that to be equal to publish subject

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and we're going to call DOT subscribe.

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Now we're going to call subscribe on next.

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So go ahead and type that.

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And then inside of these curly brackets we're going to do something we're going to go ahead and call

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print and we're going to use dollar signs 0 to print out whatever we have in our published subject.

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And as it runs you'll see it will print out the halo value that we have pushed in with on next.

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Now you're probably thinking well wait a minute.

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Why is nothing showing up.

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Why is nothing printing.

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The reason for that is because a published subject works in a very special way a published subject is

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going to show you all events but only the ones that occur after you subscribe.

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OK so anything that happens before a subscription will not be called so I can do this again.

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I could say publish subject on next and I could say world.

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You'll notice nothing gets printed but watch what happens after the subscription.

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If I type publish subject on next and I can say hello and as you can see it prints out hello because

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we added this using on next after we subscribed.

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Now I could do it again publish subject on next and I can say again hello again.

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So as you can see it prints out hello and again but it's ignoring everything that happens before we

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subscribed.

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So that is what makes a published subject unique.

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If you subscribe to it you will get all the events that are going to happen after the subscription.

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Now I want to create a new subscription here to show you what happens when you're dealing with multiple

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subscriptions.

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So go ahead and call Let pub sub subscription too and we're going to make a new subscription here.

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So using published subject let's say we want to use the same subject we can call DOT subscribe and we

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can call on next.

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Now using curly brackets I can go in here and inside the subscribe on next closure I can do the same

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thing.

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I can print dollar signs zero.

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Now you'll notice nothing is going to print for pub sub.

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But what I can do is call publish subject on next and I can say both subscriptions get this message

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and watch what happens.

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Both subscriptions printed because this happened after both subscriptions what happened before did not

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get to the first one.

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What happened after did not get to the second one because these were all before the second subscription.

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But if I call on next after both both subscriptions get the same message so there are lots of really

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cool ways that publish subjects can be used.

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It shows everything after a certain point of subscription.

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Pretty neat.

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So this is a brief overview of published subjects.

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It's a specific kind of observer where you can add in values you can make subscriptions.

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But the only values that will actually be noticed and used when subscribing are ones that occur after

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the subscription asynchronously.

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So this is published subjects in the next video we're going to talk about behavior subjects which are

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similar but quite different.

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So I'll see in the next video.

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Awesome job with this one guys.