Kotlin : error: unresolved reference for a method inside a sealed class

Question

这个小代码给出 错误：未解决的引用：make :

sealed class Color () {
    object Red : Color()
    object Blue : Color()

   override fun toString(): String =
       when (this) {
           is Red -> "Red"
           is Blue -> "Blue"
       else -> "Error"
       }

   fun make(name: String): Color {
       return when (name) {
           "Red" -> Red 
           "Blue" -> Blue
       else -> throw Exception ("Error unkown color '$name'") 
       }
   }
}   

fun main(args: Array<String>) {
    val color = Color.make("Red")
    println (color.toString())
}

我尝试了 val color = make("Red") 并得到了同样的错误。为什么？我需要做些什么来解决这个问题？

Answer 1

将函数放在伴随对象中：

sealed class Color() {
    object Red : Color()
    object Blue : Color()

    override fun toString(): String = when (this) {
        is Red -> "Red"
        is Blue -> "Blue"
        else -> "Error"
    }

    companion object {
        fun make(name: String): Color = when (name) {
            "Red" -> Red
            "Blue" -> Blue
            else -> throw Exception("Error unkown color '$name'")
        }
    }
}

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Kotlin : error: unresolved reference for a method inside a sealed class

Kotlin : error: unresolved reference for a method inside a sealed class

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