如何创建可以具有任何类型输出的 PassthroughSubject？

Question

我想创建一个可以发送任何类型的输出的 PassthroughSubject 对象。在代码中，我目前有这样的内容：

let cmd1Subj = PassthroughSubject<String, Never>()
let cmd2Subj = PassthroughSubject<String, Never>()
var desiredCmd: PassthroughSubject<String, Never>?
let executeDesiredCmdSubj = PassthroughSubject<String, Never>()
var arg: String?

func executeDesiredCmd(cmdArg: String) -> AnyPublisher<String, Never> {
    guard (desiredCmd != nil) else {
        return Just("Nothing to execute\n").eraseToAnyPublisher()
    }
    desiredCmd?.send(cmdArg)
    return Just("Executed: \(String(describing: desiredCmd)) with argument: \(cmdArg)").eraseToAnyPublisher()
}

let cancellable = executeDesiredCmdSubj
    .flatMap(executeDesiredCmd)
    .receive(on: DispatchQueue.main)
    .sink(receiveValue: {
        print($0)
    })

desiredCmd = cmd1Subj
arg = "This is the argument for command 1"
desiredCmd?.send(arg!)
desiredCmd = cmd2Subj
arg = "This is the argument for command 2"
desiredCmd?.send(arg!)

如何更改 desiredCmd 和 executeDesiredCmdSubj 以便它们可以发送运行时确定的任何类型的输出？我想做这样的事情：

let cmd1Subj = PassthroughSubject<Int, Never>()
let cmd2Subj = PassthroughSubject<String, Never>()
var desiredCmd: PassthroughSubject<Some_Generic_Type, Never>?
let executeDesiredCmdSubj = PassthroughSubject<Some_Generic_Type, Never>()
var arg: Some_Generic_Type?

func executeDesiredCmd(cmdArg: Some_Generic_Type) -> AnyPublisher<String, Never> {
    guard (desiredCmd != nil) else {
        return Just("Nothing to execute\n").eraseToAnyPublisher()
    }
    desiredCmd?.send(cmdArg)
    return Just("Executed: \(String(describing: desiredCmd)) with argument: \(cmdArg)").eraseToAnyPublisher()
}

let cancellable = executeDesiredCmdSubj
    .flatMap(executeDesiredCmd)
    .receive(on: DispatchQueue.main)
    .sink(receiveValue: {
        print($0)
    })

desiredCmd = cmd1Subj
arg = 12345
desiredCmd?.send(arg!)
desiredCmd = cmd2Subj
arg = "This is the argument for command 2"
desiredCmd?.send(arg!)

其中 Some_Generic_Type 是一个占位符，可用于表示我尝试通过 PassthroughSubject 传递的任何类型。我尝试使用“Any”作为占位符，但它产生了几个编译错误：

• “无法分配类型 'PassthroughSubject' 的值”输入“PassthroughSubject<任何，从不>”
• “无法分配“PassthroughSubject”类型的值输入“PassthroughSubject<任何，从不>”

Answer 1

我可以通过创建一个定义几个具有关联值的枚举的结构来做到这一点：

struct VersatilePassthroughSubject {
    enum SubjectOutputType {
        case subjAsStringOutput(PassthroughSubject<String, Never>)
        case subjAsIntOutput(PassthroughSubject<Int, Never>)
    }
    
    enum Arg {
        case argAsString(String)
        case argAsInt(Int)
    }
    
    var subj: SubjectOutputType? = nil
    var arg: Arg? = nil
}

let cmd1Subj = PassthroughSubject<Int, Never>()
let cmd2Subj = PassthroughSubject<String, Never>()
var desiredCmd: VersatilePassthroughSubject = VersatilePassthroughSubject()
let executeDesiredCmdSubj = PassthroughSubject<Void, Never>()

func executeDesiredCmd() -> AnyPublisher<String, Never> {
    guard (desiredCmd.subj != nil) else {
        return Just("Nothing to execute\n").eraseToAnyPublisher()
    }
    if case .subjAsIntOutput(let subj) = desiredCmd.subj {
        if case .argAsInt(let arg) = desiredCmd.arg {
            subj.send(arg)
            return Just("Executed: \(String(describing: desiredCmd)) with argument: \(arg)").eraseToAnyPublisher()
        }
    }
    else if case .subjAsStringOutput(let subj) = desiredCmd.subj {
        if case .argAsString(let arg) = desiredCmd.arg {
            subj.send(arg)
            return Just("Executed: \(String(describing: desiredCmd)) with argument: \(arg)").eraseToAnyPublisher()
        }
    }
    return Just("Nothing to execute\n").eraseToAnyPublisher()
}

let cancellable = executeDesiredCmdSubj
    .flatMap(executeDesiredCmd)
    .receive(on: DispatchQueue.main)
    .sink(receiveValue: {
        print($0)
    })

desiredCmd.subj = .subjAsIntOutput(cmd1Subj)
desiredCmd.arg = .argAsInt(12345)
executeDesiredCmdSubj.send()
desiredCmd.subj = .subjAsStringOutput(cmd2Subj)
desiredCmd.arg = .argAsString("This is the argument for command 2")
executeDesiredCmdSubj.send()