differential programming at kotlin

DiffProgramming01.kt

interface AFunctionExecutor {
    fun execute(tag: String = "None", name: String = "Taro", age: Int=32)
}

class DefaultFunctionExecutor : AFunctionExecutor {
    override fun execute(tag: String , name: String, age: Int)  = println("[$tag] $name($age)")
}

class SoccerFunctionExecutor : AFunctionExecutor {
    override fun execute(tag: String, name: String, age: Int) {
        println("[SOCCER] $name($age)")
    }
}

class VolleyBallFunctionExecutor : AFunctionExecutor {
    override fun execute(tag: String, name: String, age: Int) {
        println("[VOLLEYBALL] $name($age)")
    }
}

fun main(args: Array<String>) {
    val choseExecutorBy = fun(subject: Subject) = when(subject) {
        Subject.SOCCER -> SoccerFunctionExecutor()
        Subject.VOLLEY -> VolleyBallFunctionExecutor()
        Subject.DEFAULT -> DefaultFunctionExecutor()
    }

    val executor = choseExecutorBy(Subject.SOCCER)
    executor.execute(name = "Neko", age = 3) // [SOCCER] Neko(3)
}

enum class Subject {
    SOCCER, VOLLEY, DEFAULT
}

DiffProgramming02.kt

interface AFunctionExecutor {
    fun execute(tag: String = "None", name: String = "Taro", age: Int=32)
}

class DefaultFunctionExecutor(private val tagProvider: (() -> String)? = null) : AFunctionExecutor {
    override fun execute(tag: String, name: String, age: Int) =
            println("[${ tagProvider?.let { tagProvider.invoke() } ?: tag }] $name($age)")
}

class DelegationExecutor(private val default: DefaultFunctionExecutor): AFunctionExecutor by default

fun main(args: Array<String>) {
    val choseExecutorBy = fun(subject: Subject) = when(subject) {
        Subject.SOCCER -> DelegationExecutor(DefaultFunctionExecutor { "SOCCER" })
        Subject.VOLLEY -> DelegationExecutor(DefaultFunctionExecutor { "VOLLEY" })
        Subject.DEFAULT -> DelegationExecutor(DefaultFunctionExecutor())
    }

    val executor = choseExecutorBy(Subject.SOCCER)
    executor.execute(name = "Neko", age = 3) // [SOCCER] Neko(3)
}

enum class Subject {
    SOCCER, VOLLEY, DEFAULT
}