-
操作符
- collect
- map(_:)
- 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<AnyCancellable>()
var subscriptions = Set<AnyCancellable>()
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
*/
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<String, Never>()
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<Chatter, Never>(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<Int, Never>()
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<Int, Never>()
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<Void, Never>()
let taps = PassthroughSubject<Int, Never>()
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<Int, Never>()
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<Int, Never>()
let publisher2 = PassthroughSubject<Int, Never>()
let publisher3 = PassthroughSubject<Int, Never>()
let publishers = PassthroughSubject<PassthroughSubject<Int, Never>, 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<Int, Never>()
let publisher2 = PassthroughSubject<Int, Never>()
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<Int, Never>()
let publisher2 = PassthroughSubject<String, Never>()
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<Int, Never>()
let publisher2 = PassthroughSubject<String, Never>()
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<AnyCancellable>()
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<String,Never>()
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<String,Never>()
//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
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