combine2.swift

import Cocoa
import Combine

// ## Subjects
// A `Subject` is a special publisher that enables you to inject values into a stream.
// Just call the `send(_:)` method.
// "This can be useful for adapting existing imperative code to the Combine model."

// WHAT'S THERE:

// A publisher that exposes a method for outside callers to publish elements.
// Subject

// A subject that broadcasts elements to downstream subscribers.
// PassthroughSubject

// A subject that wraps a single value and publishes a new element whenever the value changes.
// CurrentValueSubject

// Let's send Strings! PassthroughSubject only sends values for AFTER subscription
let passthroughSubject = PassthroughSubject<String,Error>()
passthroughSubject.send("foo")

struct SomethingBad: Error, CustomStringConvertible {
    var description: String = "Bad"
}

// If you uncomment this, you will either finish or get the error to handle as the finish
// state is _already_ in place.
/*
switch Bool.random() {
case true: // Success
    passthroughSubject.send(completion: .finished)
case false: // Error
    passthroughSubject.send(completion: .failure(SomethingBad()))
}
*/

passthroughSubject.send("Hello")
passthroughSubject.sink { completionInfo in
    switch completionInfo {
    case .finished: print("Done!!")
    case .failure(let error): print("Error: \(error)")
    }
} receiveValue: { stringElement in
    print(stringElement, "received")
}
passthroughSubject.send("World")

// So this is a kind of crappy example, so next build a better passthrough example using an async data source.