操作符
- collect
- map(_:)
- print
- tryMap
- flatMap
- compactMap
- replaceNil(with:)
- replaceEmpty(with:)
- scan(::)
- tryScan
- Filtering
- removeDuplicates
- ignoreOutput
- compactMap
- first(where:)
- last(where:)
- dropFirst
- drop(while:)
- drop(untilOutputFrom:)
- prefix
- prefix(while:)
- prefix(untilOutputFrom:)
- prepend
- prepend(Sequence)
- prepend(Publisher)
- append()
- append(Sequence)
- append(Publisher)
- switchToLatest
- merge(with:)
- combineLatest
- zip
- delay(for）
- Collect
- Debounce(for)
- throttle
- Timeout
- Measuring time
- min
- max
- first
- last
- output(in:)
- count
- contains
- reduce

操作符

本文将介绍Combine中的各类运算符，这些运算符不要求你能够立即掌握，只要记得有某种运算符具有某种作用，在实际编程中可以将本文作为文档查询（ps:作者在使用RXSwift时也会经常查询某些不常用的操作符）
正如Swift标准库中对数组的操作符(map、filter、zip...)一样，publisher也有着变形、筛选、链接等等操作符

collect

本操作符将单个元素缓存到集合中(可以指定缓存个数，满足个数或者收到完成事件后)，然后发送集合

15785495862104.jpg

var subscriptions = Set()
var subscriptions = Set()
example(of: "collect") {
    ["A", "B", "C", "D", "E"].publisher
//        .collect()
//        .collect(2)
        .sink(receiveCompletion: { print($0) },
              receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: collect ———
A
B
C
D
E
finished

// 打开.collect()注释
——— Example of: collect ———
["A", "B", "C", "D", "E"]
finished

// 注释掉.collect()打开.collect(2)注释
——— Example of: collect ———
["A", "B"]
["C", "D"]
["E"]
finished
*/

使用.collect和其他没有指定个数或缓存大小的操作符时，注意他们讲使用没有内存大小限制的缓存区存储收到的元素。注意内存溢出

map(_:)

和Swift标准库中集合的Map类似，使用函数、闭包、或者keyPath来转变值

/// 将数字转换成对应的ASCll值的字符，无法转换时返回空字符
func numToString(num: Int) -> String {
    .init(Character(Unicode.Scalar(num) ?? "\0"))
}
example(of: "map") {
    (65...67)
        .publisher
        .map(numToString(num:))
        .print()
        .map(\.localizedLowercase)
        .sink(receiveCompletion: { print($0) }, receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: map ———
receive subscription: (["A", "B", "C", "D", "E"])
request unlimited
receive value: (A)
a
receive value: (B)
b
receive value: (C)
c
receive finished
finished
*/

print

打印接受到的值或者完成事件，通常用在调试的时候

tryMap

包括map在内的几个操作符都有一个对应的try操作符，该操作符将接受可能引发错误的闭包。如果有错误抛出，它将发送错误完成事件

example(of: "tryMap") {
    let publisher = PassthroughSubject()

    publisher
        .tryMap { try JSONSerialization.jsonObject(with: $0.data(using: .utf8)!, options: .allowFragments) }
        .sink(receiveCompletion: { print($0) },
              receiveValue: { print($0) })
        .store(in: &subscriptions)

    publisher.send(#"{"name":"DKJone"}"#)
    publisher.send("not a JSON")
}

/* 输出
——— Example of: tryMap ———
{
    name = DKJone;
}
failure(Error Domain=NSCocoaErrorDomain Code=3840 ...."})
*/

此处使用的#""#为原始字符串更多内容查看Swift5新特性 & XCode 10.2更新

flatMap

在swift标准库中FlatMap用来使多为数组扁平化为一位数组，并且在swift4.1中被重命名为Swift 4.1中被重命名为compactMap，在Combine中flatmap的作用稍微有点不同。
flatmap作用是在publisher内部仍然包含publisher时可以将事件扁平化，具体查看以下代码：

example(of: "flatMap") {
    // 1 定义三个人用于聊天
    let 小明 = Chatter(name: "小明", message: "小明: 鄙人王小明!")
    let 老王 = Chatter(name: "老王", message: "老王: 我就是隔壁老王!")
    let 于大爷 = Chatter(name: "于大爷", message: "烫头去")

    // 2 j可以获取当前值的Publishers初始值是小明
    let chat = CurrentValueSubject(小明)

//    chat
//        .flatMap(maxPublishers: .max(2)) { $0.message }
//        .sink(receiveValue: { print($0) })
//        .store(in: &subscriptions)

    chat.sink{ print($0.message.value)}

    小明.message.value = "小明: 马冬梅在家吗？"
    chat.value = 老王
    老王.message.value = "老王: 什么冬梅？"
    小明.message.value = "小明: 马冬梅啊！"
    chat.value = 于大爷
    老王.message.value = "老王: 马东什么？"
}

/* 输出
——— Example of: flatMap ———
小明: 鄙人王小明!
老王: 我就是隔壁老王!
烫头去

// 注释chat.sink{ print($0.message.value)}打开上放订阅的注释输出
——— Example of: flatMap ———
小明: 鄙人王小明!
小明: 马冬梅在家吗？
老王: 我就是隔壁老王!
老王: 什么冬梅？
小明: 马冬梅啊！
老王: 马东什么？
*/

在一开始我们使用chat.sink{ print($0.message.value)}订阅事输出只有三句话，这是因为我们只对chat进行了订阅。当具体的Chatter的message变化时，我们并不能订阅到事件。那我想订阅全部的谈话事件怎么办呢？flatMap正是为此而生的，当我们改成flatmap的订阅后可以输出所有publisher的事件，包括publisher的值内部的publisher发出的事件。上面我们也提到，map操作会缓存publisher，为了防止我们缓存太多的publisher我们可以在flatmap事指定缓存的publisher个数(maxPublishers: .max(2))，所以于老师并没有被没缓存，也就没有发出于老师说话的事件。如果未指定个数，则maxPublishers默认为.unlimited。

15785615311395.jpg

compactMap

和swift标准库中的数组操作符一样，如果你在转换时不需要转换失败的nil值，你使用此方法将的到一个没有可选值的序列

example(of: "compactMap") {
    let strings = ["a", "1.24", "3", "def", "45", "0.23"].publisher

    // 2
    strings
        .compactMap { Float($0) }
        .sink(receiveValue: { print($0)})
        .store(in: &subscriptions)
}
/* 输出
——— Example of: compactMap ———
1.24
3.0
45.0
0.23
*/

replaceNil(with:)

对的它的作用和方法名一样直白，就是在遇到可选值为空时用默认值替换空值,原始的序列也变成一个非空序列

example(of: "replaceNil") {
  ["A", nil, "C"].publisher
    .replaceNil(with: "-")
    .map { $0! }
    .sink(receiveValue: { print($0) }) 
    .store(in: &subscriptions)
}
/* 输出
——— Example of: replaceNil ———
A
-
C
*/

replaceEmpty(with:)

替换空序列

example(of: "replaceEmpty(with:)") {
  let empty = Empty()
  empty
    .replaceEmpty(with: 1)
    .sink(receiveCompletion: { print($0) },
          receiveValue: { print($0) })
    .store(in: &subscriptions)
}

Empty：创建一个只发出完成事件的序列

scan(::)

扫描之前的序列中所有元素，运用函数计算新值，接收一个初始值和每次接受到新元素的函数

example(of: "scan") {
    // 1 一共进了10个球 每个球进球得分随机1~3分，每次进球后打印当前总分
    let score = (1..<10).compactMap { _ in (1...3).randomElement() }
    score
        .publisher
        .print()
        .scan(0, +)
        .sink(receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: scan ———
receive subscription: ([1, 1, 2, 1, 1, 2, 3, 1, 3])
request unlimited
receive value: (1)
1
receive value: (1)
2
receive value: (2)
4
receive value: (1)
5
receive value: (1)
6
receive value: (2)
8
receive value: (3)
11
receive value: (1)
12
receive value: (3)
15
receive finished
*/

注意.scan(0, +)这里的 + 是一个函数,你可以在Xcode点击查看其声明
public static func + (lhs: Int, rhs: Int) -> Int

tryScan

作为一名有经验的程序员，你应该能自己联想到他的功能，对就是你想的那样。

在后面的操作符中如果没有特殊功能将不再单独介绍相关的try运算符，但我会告诉你它的存在

Filtering

和标准库的Array的方法一样，该方法也是接受一个返回Bool值的函数过滤元素，返回false的值将被过滤掉

example(of: "filter") {
    let numbers = [(1,2),(2,4),(3,1),(6,2),(1,0)].publisher

    // 过滤掉第一个值小于第二个值的元祖
    numbers
        .filter( > )
        .sink(receiveValue: { print("\($0) 大于 \($1)") })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: filter ———
3 大于 1
6 大于 2
1 大于 0
*/

注意此处的 >是一个函数，这里的参数可以是函数（或者闭包-匿名函数）
public static func > (lhs: Int, rhs: Int) -> Bool

removeDuplicates

过滤掉连续的重复值

15828721202656.jpg

example(of: "removeDuplicates") {
    // 1
    let userInput = ["aaa", "aaa", "bbbb", "ccc", "bbbb"].publisher

    // 2
    userInput
        .removeDuplicates()
        .sink(receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: removeDuplicates ———
aaa
bbbb
ccc
bbbb
*/

ignoreOutput

忽略发送的值，如果有的时候你只在乎publisher有没有完成发送二不关心他具体发送了那些值，可已使用ignoreOutput，使用后将只会订阅到完成事件（错误完成或者正常结束）

example(of: "ignoreOutput") {
    // 1
    let numbers = (1...10_000).publisher
    // 2
    numbers
        .ignoreOutput()
        .sink(receiveCompletion: { print("Completed with: \($0)") },
              receiveValue: { print($0) })
        .store(in: &subscriptions)
}

/* 输出
——— Example of: ignoreOutput ———
Completed with: finished
*/

compactMap

转换时忽略掉无法转换的值，和标准库中的Array 的同名方法类似

example(of: "compactMap") {
    let strings = ["http://www.baidu.com", "dkjone://happy.lv", "哈利路亚", "", "https://127.0.0.1"].publisher

    strings
        .compactMap(URL.init(string:))
        .sink(receiveValue: { print($0.absoluteString) })
        .store(in: &subscriptions)
}

/* 输出
——— Example of: compactMap ———
http://www.baidu.com
dkjone://happy.lv
https://127.0.0.1
*/

first(where:)

找到序列中的第一个满足条件的值然后发出，并且发送完成事件，取消上游的publishers继续向其发送值

example(of: "first(where:)") {
    let numbers = (1...9).publisher
    numbers
        .print("numbers")
        .first(where: { $0 % 2 == 0 })
        .sink(receiveCompletion: { print("Completed with: \($0)") },
              receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: first(where:) ———
numbers: receive subscription: (1...9)
numbers: request unlimited
numbers: receive value: (1)
numbers: receive value: (2)
numbers: receive cancel
2
Completed with: finished
*/

last(where:)

与first(where:)相反，此运算符是贪婪的，因为它必须等待所有值发出，才能知道是否找到匹配的值。因此，上游必须是一个已经经完成的publisher

example(of: "last(where:)") {
    let numbers = PassthroughSubject()
    numbers
        .last(where: { $0 % 2 == 0 })
        .sink(receiveCompletion: { print("Completed with: \($0)") },
              receiveValue: { print($0) })
        .store(in: &subscriptions)

    numbers.send(1)
    numbers.send(2)
    numbers.send(3)
    numbers.send(4)
    numbers.send(5)
    numbers.send(completion: .finished)
}
/* 输出
——— Example of: last(where:) ———
4
Completed with: finished
*/

dropFirst

忽略指定个数的值

example(of: "dropFirst") {
    let numbers = (1...10).publisher
    numbers
        .dropFirst(8)
        .sink(receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: dropFirst ———
9
10
*/

drop(while:)

忽略序列中的值直到满足条件时。

 example(of: "drop(while:)") {
    let numbers = (1...10).publisher
    numbers
        .drop(while: { $0 % 5 != 0 })
        .sink(receiveValue: { print($0) })
        .store(in: &subscriptions)
}

/* 输出
——— Example of: drop(while:) ———
5
6
7
*/

drop(untilOutputFrom:)

忽略序列中对的值直到另一个序列开始发送值

 example(of: "drop(untilOutputFrom:)") {
    let isReady = PassthroughSubject()
    let taps = PassthroughSubject()

    taps
        .drop(untilOutputFrom: isReady)
        .sink(receiveValue: {
            print($0)
        })
        .store(in: &subscriptions)

    (1...5).forEach { n in
        taps.send(n)
        if n == 3 {
            isReady.send()
        }
    }
}
/* 输出
——— Example of: drop(untilOutputFrom:) ———
4
5
*/

prefix

获取序列中指定个数的值，然后发出完成事件

 example(of: "prefix") {
    let numbers = (1...10).publisher
    numbers
        .prefix(2)
        .sink(receiveCompletion: { print("Completed with: \($0)") },
              receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: prefix ———
1
2
Completed with: finished
*/

prefix(while:)

获取序列中的值直到满足给定的条件，然后发出完成事件，与 drop(while:)相反

15828722470169.jpg

prefix(untilOutputFrom:)

获取序列中的值直到给定的序列发出值，然后发出完成事件，与 drop(untilOutputFrom:)相反

15828722334301.jpg

prepend

在原始的publisher序列前面追加给定的值，值的类型必须与原始序列类型一致

15828726074065.jpg

 example(of: "prepend(Output...)") {
  let publisher = [3, 4].publisher
  publisher
    .prepend(1, 2)
    .sink(receiveValue: { print($0) })
    .store(in: &subscriptions)
}
/* 输出
——— Example of: prepend(Output...) ———
1
2
3
4
*/

prepend(Sequence)

在原始的publisher序列前面追加给定序列中的所有值，值的类型必须与原始序列类型一致

prepend(Publisher)

在原始的publisher序列前面追加给定publisher 序列中的所有值，值的类型必须与原始序列类型一致，如果追加的publisher是一个未完成的序列，会等新追加序列发送完成事件再发送原始序列中的值

example(of: "prepend(Publisher) #2") {
  let publisher1 = [3, 4].publisher
  let publisher2 = PassthroughSubject()

  publisher1
    .prepend(publisher2)
    .sink(receiveValue: { print($0) })
    .store(in: &subscriptions)

  publisher2.send(1)
  publisher2.send(2)
//  publisher2.send(completion: .finished)
}
/* 输出
——— Example of: prepend(Publisher) ———
1
2

//打开最后一行注释后输出
——— Example of: prepend(Publisher) ———
1
2
3
4
*/

append()

与prepend() 类似，只是位置改为在原始序列末尾追加

append(Sequence)

与prepend(Sequence) 类似，只是位置改为在原始序列末尾追加

15828732022683.jpg

 example(of: "append(Output...)") {
    let publisher = [1].publisher

    publisher
        .append(2, 3)
        .append(4)
        .sink(receiveValue: { print($0) })
        .store(in: &subscriptions)
}
/* 输出
——— Example of: append(Output...) ———
1
2
3
4
*/

append(Publisher)

与prepend(Publisher) 类似，只是位置改为在原始序列末尾追加

switchToLatest

从一个publiser切换到另一个，这会停止接收之前publisher的值而改成接收新切换的publisher序列中的值

15828737758818.jpg

 example(of: "switchToLatest") {
    let publisher1 = PassthroughSubject()
    let publisher2 = PassthroughSubject()
    let publisher3 = PassthroughSubject()

    let publishers = PassthroughSubject, Never>()

    publishers
        .switchToLatest()
        .sink(receiveCompletion: { _ in print("Completed!") },
              receiveValue: { print($0) })
        .store(in: &subscriptions)

    publishers.send(publisher1)
    publisher1.send(1)
    publisher1.send(2)

    publishers.send(publisher2)
    publisher1.send(3)
    publisher2.send(4)
    publisher2.send(5)

    publishers.send(publisher3)
    publisher2.send(6)
    publisher3.send(7)
    publisher3.send(8)
    publisher3.send(9)

    publisher3.send(completion: .finished)
    publishers.send(completion: .finished)
}
/* 输出
——— Example of: switchToLatest ———
1
2
4
5
7
8
9
Completed!
*/

merge(with:)

与RXSwift中的同名操作符效果一致，将publishers中的值按时间顺序合并成一个publisher，值类型必须一致

image

example(of: "merge(with:)") {
    let publisher1 = PassthroughSubject()
    let publisher2 = PassthroughSubject()

    publisher1
        .merge(with: publisher2)
        .sink(receiveCompletion: { _ in print("Completed") },
              receiveValue: { print($0) })
        .store(in: &subscriptions)

    publisher1.send(1)
    publisher1.send(2)

    publisher2.send(3)

    publisher1.send(4)

    publisher2.send(5)

    publisher1.send(completion: .finished)
    publisher2.send(completion: .finished)
}

/* 输出
——— Example of: merge(with:) ———
1
2
3
4
5
Completed
*/

combineLatest

与RXSwift中的同名操作符效果一致，当多个 publisher 中任何一个发出一个元素，就发出一个元素。这个元素是由这些 publisher 中最新的元素组合起来的元组，各个publisher的值类型可以不一样

15828766695342.jpg

example(of: "combineLatest") {
    let publisher1 = PassthroughSubject()
    let publisher2 = PassthroughSubject()

    publisher1
        .combineLatest(publisher2)
        .sink(receiveCompletion: { _ in print("Completed") },
              receiveValue: { print("P1: \($0), P2: \($1)") })
        .store(in: &subscriptions)

    publisher1.send(1)
    publisher1.send(2)

    publisher2.send("a")
    publisher2.send("b")

    publisher1.send(3)

    publisher2.send("c")

    publisher1.send(completion: .finished)
    publisher2.send(completion: .finished)
}

/* 输出
——— Example of: combineLatest ———
P1: 2, P2: a
P1: 2, P2: b
P1: 3, P2: b
P1: 3, P2: c
Completed
*/

zip

与swift标准库和RXSwift的同名函数左营类似，在publisher相同索引处发出成对值的元组。它等待每个publisher发出一个值，然后在所有publisher在当前索引处发出一个元素后发出一个值的元组。这意味着，如果zip两个publisher，则每次两个发布服务器都发出一个值时，才会发出一个元组。

image

example(of: "zip") {
    let publisher1 = PassthroughSubject()
    let publisher2 = PassthroughSubject()

    publisher1
        .zip(publisher2)
        .sink(receiveCompletion: { _ in print("Completed") },
              receiveValue: { print("P1: \($0), P2: \($1)") })
        .store(in: &subscriptions)

    publisher1.send(1)
    publisher1.send(2)

    publisher2.send("a")
    publisher2.send("b")

    publisher1.send(3)

    publisher2.send("c")
    publisher2.send("d")

    publisher1.send(completion: .finished)
    publisher2.send(completion: .finished)
}

/* 输出
——— Example of: zip ———
P1: 1, P2: a
P1: 2, P2: b
P1: 3, P2: c
Completed
*/

delay(for）

延迟发出元素，接受一个延迟时间参数,以及要运行的线程

var subscriptions = Set()
let start = Date()
let deltaFormatter: NumberFormatter = {
    let f = NumberFormatter()
    f.negativePrefix = ""
    f.minimumFractionDigits = 1
    f.maximumFractionDigits = 1
    return f
}()

/// 本页代码运行时初始化时间， 计算运行到固定行数时得到时间差
public var deltaTime: String {
    return deltaFormatter.string(for: Date().timeIntervalSince(start))!
}

example(of: "Delay") {
    let publisher = Timer.publish(every: 1, on: .main, in: .common).autoconnect()

    publisher.sink { date in
        print("origin:\t" + "\(deltaTime)\t" + date.description)
    }.store(in: &subscriptions)

    publisher.delay(for: .seconds(2), scheduler: DispatchQueue.main).sink { date in
        print("delay:\t" + "\(deltaTime)\t" + date.description)
    }.store(in: &subscriptions)
}

/* 输出
——— Example of: Delay ———
origin: 1.1 2020-03-02 06:33:55 +0000
origin: 2.1 2020-03-02 06:33:56 +0000
origin: 3.1 2020-03-02 06:33:57 +0000
delay:  3.3 2020-03-02 06:33:55 +0000
origin: 4.1 2020-03-02 06:33:58 +0000
delay:  4.1 2020-03-02 06:33:56 +0000
...
*/

autoconnect() 在第一次订阅时立即连接。

Collect

将原始序列中的元素组成集合发出，可以接受的参数有集合个数、时间、个数或时间。满足参数条件就会发出集合，否则等待元素。（参数是时间和个数都设置时满足任一就会发出）

example(of: "Collect") {
    let publisher = Timer.publish(every: 1, on: .main, in: .common).autoconnect()

    publisher.sink { date in
        print("origin:\t" + "\(deltaTime)\t" + date.description)
    }.store(in: &subscriptions)

    publisher.collect(.byTimeOrCount(DispatchQueue.main, .seconds(5), 3), options: .none) .sink { date in
        print("collect:\t" + "\(deltaTime)\t" + date.description)
    }.store(in: &subscriptions)
}
/* 输出
——— Example of: Collect ———
origin: 1.1 2020-03-02 07:38:26 +0000
origin: 2.1 2020-03-02 07:38:27 +0000
origin: 3.1 2020-03-02 07:38:28 +0000
collect:    3.1 [2020-03-02 07:38:26 +0000, 2020-03-02 07:38:27 +0000, 2020-03-02 07:38:28 +0000]
origin: 4.1 2020-03-02 07:38:29 +0000
origin: 5.1 2020-03-02 07:38:30 +0000
collect:    5.1 [2020-03-02 07:38:29 +0000, 2020-03-02 07:38:30 +0000]
...
*/

Debounce(for)

与RXSwift同名操作符作用一致，等待多长时间后没有新值再发出该值，忽略中间连续变化的值

debonce

example(of: "Debounce") {
   let publisher = PassthroughSubject()
   let typingHelloWorld: [(TimeInterval, String)] = [
      (0.0, "H"),
      (0.1, "He"),
      (0.2, "Hel"),
      (0.3, "Hell"),
      (0.5, "Hello"),
      (0.6, "Hello "),
      (2.0, "Hello W"),
      (2.1, "Hello Wo"),
      (2.2, "Hello Wor"),
      (2.4, "Hello Worl"),
      (2.5, "Hello World")
    ]
    //模拟输入Hello Word
    typingHelloWorld.forEach { (delay,str) in
        DispatchQueue.main.asyncAfter(deadline: .now() + delay) {
            publisher.send(str)
        }
    }

    publisher.sink { data in
        print("origin:\t" + "\(deltaTime)\t" + data)
    }.store(in: &subscriptions)

    publisher.debounce(for: .seconds(1), scheduler: DispatchQueue.main).sink { data in
        print("debounce:\t" + "\(deltaTime)\t" + data)
    }.store(in: &subscriptions)
}

/* 输出
——— Example of: Debounce ———
origin: 0.1 H
origin: 0.2 He
origin: 0.3 Hel
origin: 0.4 Hell
origin: 0.6 Hello
origin: 0.7 Hello 
debounce:   1.7 Hello 
origin: 2.2 Hello W
origin: 2.2 Hello Wo
origin: 2.5 Hello Wor
origin: 2.5 Hello Worl
origin: 2.8 Hello World
debounce:   3.8 Hello World
*/

throttle

与RXSwift同名操作符效果一致，在固定时间内只发出一个值，过滤掉其他值，你可以选择最新的值或者第一个值发出

example(of: "throttle") {
   let publisher = PassthroughSubject()

    //模拟输入Hello Word
    typingHelloWorld.forEach { (delay,str) in
        DispatchQueue.main.asyncAfter(deadline: .now() + delay) {
            publisher.send(str)
        }
    }

    publisher.sink { data in
        print("origin:\t" + "\(deltaTime)\t" + data)
    }.store(in: &subscriptions)

    publisher.throttle(for: .seconds(1), scheduler: DispatchQueue.main, latest: false).sink { data in
        print("throttle:\t" + "\(deltaTime)\t" + data)
    }.store(in: &subscriptions)
}
/* 输出
——— Example of: throttle ———
origin: 0.1 H
throttle:   0.1 H
origin: 0.2 He
origin: 0.3 Hel
origin: 0.4 Hell
origin: 0.6 Hello
origin: 0.7 Hello 
throttle:   1.2 Hello 
origin: 2.2 Hello W
origin: 2.2 Hello Wo
throttle:   2.2 Hello Wo
origin: 2.5 Hello Wor
origin: 2.5 Hello Worl
origin: 2.8 Hello World
throttle:   3.5 Hello World
*/

Timeout

与RXSwift同名操作符一样，超出给定的时间后发出结束事件，你可以给出自定义错误类型，这样在超时后会发出错误完成事件

image

Measuring time

用于调试的操作符，计算两次值发出的时间间隔，单位是纳秒

min

发出原始序列中的最小值，然后发出完成事件。要求序列是已完成的序列否则会等待原始序列的完成事件。

max

与min相反，发出原始序列中的最大值，然后发出完成事件。要求序列是已完成的序列否则会等待原始序列的完成事件。

first

发出原始序列中的第一个值，然后发出完成事件

last

与first相反，发出原始序列中的最后一个值，然后发出完成事件。要求序列是已完成的序列否则会等待原始序列的完成事件。

output(in:)

output（at:）发出指定位置的值，output（in:）发出指定范围内的值

example(of: "output(in:)") {
  let publisher = ["A", "B", "C", "D", "E"].publisher
  publisher
    .print("publisher")
    .output(in: 1...3)
    .sink(receiveCompletion: { print($0) },
          receiveValue: { print("Value in range: \($0)") })
    .store(in: &subscriptions)
}
/*输出
——— Example of: output(in:) ———
publisher: receive subscription: (["A", "B", "C", "D", "E"])
publisher: request unlimited
publisher: receive value: (A)
publisher: request max: (1) (synchronous)
publisher: receive value: (B)
Value in range: B
publisher: receive value: (C)
Value in range: C
publisher: receive value: (D)
Value in range: D
publisher: receive cancel
finished
*/

count

记录原始序列发出值的个数，并发出

contains

原始publisher发出指定值，则contains运算符将发出true并取消订阅；如果原始publisher已完成且发出的值均不等于指定值，则发出false

reduce

与标准库函数类似，在原始publisher完成时发出累计计算的到的值

15832015826163.jpg

SwiftUI 与 Combine(二)

操作符

collect

map(_:)

print

tryMap

flatMap

compactMap

replaceNil(with:)

replaceEmpty(with:)

scan(::)

tryScan

Filtering

removeDuplicates

ignoreOutput

compactMap

first(where:)

last(where:)

dropFirst

drop(while:)

drop(untilOutputFrom:)

prefix

prefix(while:)

prefix(untilOutputFrom:)

prepend

prepend(Sequence)

prepend(Publisher)

append()

append(Sequence)

append(Publisher)

switchToLatest

merge(with:)

combineLatest

zip

delay(for）

Collect

Debounce(for)

throttle

Timeout

Measuring time

min

max

first

last

output(in:)

count

contains

reduce

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