Publishers and Subscribers

• A Publisher publishes values ...
• .. a subscriber subscribes to receive publisher's values

Specifics:

• Publishers are typed to the data and error types they can emit
• A publisher can emit, zero, one or more values and terminate gracefully or with an error of the type it declared.

Example 1

"publish" just one value then complete

 let publisher1 = Just(42)

// You need to _subscribe_ to receive values (here using a sink with a closure)
let subscription1 = publisher1.sink { value in
    print("Received value from publisher1: \(value)")
}

Example 2

"publish" a series of values immediately

let publisher2 = [1, 2, 3, 4, 5].publisher

let subscription2 = publisher2
    .sink { value in
        print("Received value from publisher2: \(value)")
    }

Example 3

assign publisher values to a property on an object

class MyClass {
    var property: Int = 0 {
        didSet {
            print("Did set property to \(property)")
        }
    }
}

let publisher2 = [1, 2, 3, 4, 5].publisher
let object = MyClass()
let subscription3 = publisher2.assign(to: \.property, on: object)

上篇笔记说过主要有发布者，订阅者和操作符，其中操作符并不是必须

以上3例都没有使用操作符，因为数据并不需要做其他处理即可被订阅者消费，操作符的主要作用就是做数据处理