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example-function-in-playground #19

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May 26, 2015
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example-function-in-playground
May 26, 2015
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May 26, 2015
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122 changes: 71 additions & 51 deletions OSXPlayground.playground/Contents.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -19,16 +19,18 @@ Creating an Observable is one thing, but if nothing subscribes to the observable
`empty` creates an observable that contains no objects. The only message it sends is the `.Completed` message.
*/

let emptyObservable: Observable<Int> = empty()

let emptySubscriber = emptyObservable >- subscribe { event in
switch event {
case .Next(let box):
println("\(box.value)")
case .Completed:
println("completed")
case .Error(let error):
println("\(error)")
example("Empty observable") {
let emptyObservable: Observable<Int> = empty()

let emptySubscriber = emptyObservable >- subscribe { event in
switch event {
case .Next(let box):
println("\(box.value)")
case .Completed:
println("completed")
case .Error(let error):
println("\(error)")
}
}
}

Expand All @@ -41,28 +43,33 @@ As you can see, no values are ever sent to the subscriber of an empty observable
`never` creates an observable that contains no objects and never completes or errors out.
*/

let neverObservable: Observable<String> = never()

let neverSubscriber = neverObservable >- subscribe { _ in
println("This block is never called.")
example("Never observable") {
let neverObservable: Observable<String> = never()

let neverSubscriber = neverObservable >- subscribe { _ in
println("This block is never called.")
}
}

/*:
### returnElement/just
These two functions behave identically. They send two messages to subscribers. The first message is the value and the second message is `.Complete`.
*/

let oneObservable = just(32)

let oneObservableSubscriber = oneObservable >- subscribe { event in
switch event {
case .Next(let box):
println("\(box.value)")
case .Completed:
println("completed")
case .Error(let error):
println("\(error)")
}
example("returnElement/just") {
let oneObservable = just(32)

let oneObservableSubscriber = oneObservable
>- subscribe { event in
switch event {
case .Next(let box):
println("\(box.value)")
case .Completed:
println("completed")
case .Error(let error):
println("\(error)")
}
}
}

/*:
Expand All @@ -74,16 +81,19 @@ Here we see that the `.Next` event is sent just once, then the `.Completed` even
Now we are getting to some more interesting ways to create an Observable. This function creates an observable that produces a number of values before completing.
*/

let multipleObservable = returnElements(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

let multipleObservableSubscriber = multipleObservable >- subscribe { event in
switch event {
case .Next(let box):
println("\(box.value)")
case .Completed:
println("completed")
case .Error(let error):
println("\(error)")
example("returnElements") {
let multipleObservable/* : Observable<Int> */ = returnElements(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

let multipleObservableSubscriber = multipleObservable
>- subscribe { event in
switch event {
case .Next(let box):
println("\(box.value)")
case .Completed:
println("completed")
case .Error(let error):
println("\(error)")
}
}
}

Expand All @@ -104,8 +114,11 @@ Take some time and search for code matching `-> Observable` in the RxCocoa frame
Up to this point, I have only used the `subscribe` method to listen to Observables, but there are several others.
*/

let nextOnlySubscriber = multipleObservable >- subscribeNext { value in
println("\(value)")
example("subscribeNext") {
let nextOnlySubscriber = returnElements(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
>- subscribeNext { value in
println("\(value)")
}
}

/*:
Expand All @@ -122,25 +135,30 @@ Now that you understand how to create Observables and subscribe to them. Let's l
The most common way to reduce a sequence is to apply a filter to it and the most generic of these is `where` or `filter`. You will see in the code below that the messages containing odd numbers are being removed so the subscriber wont see them.
*/

var onlyEvensSubscriber = multipleObservable
>- filter {
$0 % 2 == 0
}
>- subscribeNext { value in
println("\(value)")
example("filter") {
let onlyEvensSubscriber = returnElements(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
>- filter {
$0 % 2 == 0
}
>- subscribeNext { value in
println("\(value)")
}
}

/*:
### distinctUntilChanged
This filter tracks the last value emitted and removes like values. This function is good for reducing noise in a sequence.
*/

let distinctUntilChangedSubscriber = returnElements(1, 2, 3, 1, 1, 4)
>- distinctUntilChanged
>- subscribeNext { value in
println("\(value)")
example("distinctUntilChanged") {
let distinctUntilChangedSubscriber = returnElements(1, 2, 3, 1, 1, 4)
>- distinctUntilChanged
>- subscribeNext { value in
println("\(value)")
}
}


/*:
In the example above, the values 1, 2, 3, 1, 4 will be printed. The extra 1 will be filtered out.
There are several different versions of `distinctUntilChanged`. Have a look in the file Observable+Single.swift to review them.
Expand All @@ -153,10 +171,12 @@ There are several different versions of `distinctUntilChanged`. Have a look in t
This function will perform a function on each element in the sequence until it is completed, then send a message with the aggregate value. It works much like the Swift `reduce` function works on sequences.
*/

let aggregateSubscriber = multipleObservable
>- aggregate(0, +)
>- subscribeNext { value in
println("\(value)")
example("aggregate") {
let aggregateSubscriber = returnElements(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
>- aggregate(0, +)
>- subscribeNext { value in
println("\(value)")
}
}

/*:
Expand Down
9 changes: 6 additions & 3 deletions OSXPlayground.playground/Sources/SupportCode.swift
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Original file line number Diff line number Diff line change
@@ -1,3 +1,6 @@
//
// This file (and all other Swift source files in the Sources directory of this playground) will be precompiled into a framework which is automatically made available to OSXPlayground.playground.
//


public func example(description: String, action: () -> ()) {
println("\n--- \(description) example ---")
action()
}