[Xcode/Swift] CombineLatest vs Merge: Explained Eminem-style

Yo, what’s up, little homie? It’s your boy, Eminem, here to drop some knowledge bombs about RxSwift!

So, RxSwift is like a toolbox for writing code that does cool stuff with data streams. And two tools in that toolbox are combineLatest and merge. They’re kinda similar, but they have some differences.

Let’s start with combineLatest. Imagine you have two friends, Bob and Alice, who like to play video games. Bob’s always playing on his Xbox, and Alice is always playing on her PlayStation. Now, you want to know what game they’re playing, and you want to keep track of it in real-time. So you stand in the middle of their rooms and keep an eye on both screens at the same time.

In RxSwift, combineLatest works kinda like that. It takes two data streams, let’s call them “Stream A” and “Stream B”, and it watches them both at the same time. Whenever either Stream A or Stream B sends a new event, combineLatest combines the latest events from both streams into a single event, and gives it to you. It’s like you’re standing in the middle, keeping an eye on both streams and getting updates whenever either one changes.

Here’s some sample code to help you understand:

let streamA = Observable.just("Hello") // Stream A sends "Hello"
let streamB = Observable.just("World") // Stream B sends "World"

Observable.combineLatest(streamA, streamB)
    .subscribe(onNext: { (a, b) in
        print("\(a) \(b)")
    })
    .disposed(by: disposeBag)

// Output: "Hello World"

Now, let’s talk about merge. Imagine you have two more friends, Jay and Rihanna, who also like to play video games. But unlike Bob and Alice, Jay and Rihanna play games together on a single console, and they take turns using the controller. Jay plays for a while, then Rihanna takes over, and they keep passing the controller back and forth.

In RxSwift, merge works kinda like that. It takes two data streams, let’s call them “Stream X” and “Stream Y”, and it merges them together into a single stream. Whenever either Stream X or Stream Y sends a new event, merge passes it along to you, just like Jay and Rihanna passing the controller back and forth.

Here’s some sample code to help you understand:

let streamX = Observable.just("Slim") // Stream X sends "Slim"
let streamY = Observable.just("Shady") // Stream Y sends "Shady"

Observable.merge(streamX, streamY)
    .subscribe(onNext: { (name) in
        print(name)
    })
    .disposed(by: disposeBag)

// Output: "Slim" "Shady"

So, to sum it up, combineLatest is like keeping an eye on two separate streams and getting updates whenever either one changes, while merge is like merging two streams together into one and getting events as they come from either of them. Hope that clears things up, little homie! Keep coding and stay dope!