README.md

Command

Encapsulate a request as an object, thereby allowing for the parameterization of clients with different requests, and the queuing or logging of requests. It also allows for the support of undoable operations.

Source: wikipedia.org

Swift Example

protocol DoorCommand {
    func execute() -> String
}

class OpenCommand : DoorCommand {
    let doors:String

    required init(doors: String) {
        self.doors = doors
    }
    
    func execute() -> String {
        return "Opened \(doors)"
    }
}

class CloseCommand : DoorCommand {
    let doors:String

    required init(doors: String) {
        self.doors = doors
    }
    
    func execute() -> String {
        return "Closed \(doors)"
    }
}

class HAL9000DoorsOperations {
    let openCommand: DoorCommand
    let closeCommand: DoorCommand
    
    init(doors: String) {
        self.openCommand = OpenCommand(doors:doors)
        self.closeCommand = CloseCommand(doors:doors)
    }
    
    func close() -> String {
        return closeCommand.execute()
    }
    
    func open() -> String {
        return openCommand.execute()
    }
}

Swift Usage

let podBayDoors = "Pod Bay Doors"
let doorModule = HAL9000DoorsOperations(doors:podBayDoors)

doorModule.open()
doorModule.close()

Kotlin Example

interface OrderCommand {
    fun execute()
}

class OrderAddCommand(val id: Long) : OrderCommand {
    override fun execute() = println("adding order with id: $id")
}

class OrderPayCommand(val id: Long) : OrderCommand {
    override fun execute() = println("paying for order with id: $id")
}

class CommandProcessor {

    private val queue = ArrayList<OrderCommand>()

    fun addToQueue(orderCommand: OrderCommand): CommandProcessor
            = apply { queue.add(orderCommand) }

    fun processCommands(): CommandProcessor = apply {
        queue.forEach { it.execute() }
        queue.clear()
    }
}

Kotlin Usage

fun main(args: Array<String>) {
    CommandProcessor()
            .addToQueue(OrderAddCommand(1L))
            .addToQueue(OrderAddCommand(2L))
            .addToQueue(OrderPayCommand(2L))
            .addToQueue(OrderPayCommand(1L))
            .processCommands()
}

Summary