Why can't I launch a function in the base class of enum in kotlin in Android Studio?

In Code A, the ELevel is enum class, and the fun getLevel in the enum will return a subclass by the parameter soundValue.

The Code A can be compiled.

I think Code B is better, but in fact it can’t be compiled ,why?

Code A

data class MSoundDensity(  
    val avg: Double=0.0,
    val max: Double=0.0,
    val level: ELevel=ELevel.Whisper.getLevel(avg)    
)

enum class ELevel(val label:String){
   Whisper("Whisper"),
   Quiet("Quiet Library");

   fun getLevel(soundValue:Double):ELevel{
       var temp=Whisper
       val i=soundValue.toInt()

       if (i in 1..20){
           temp=Whisper
       }

       if (i in 21..40){
           temp=Quiet
       }

       return temp
   }

}

Code B

data class MSoundDensity(  
    val avg: Double=0.0,
    val max: Double=0.0,
    val level: ELevel=ELevel.getLevel(avg)  //It cause error when I use base class.    
)

//The same

>Solution :

Just like any other class, you have to put that function in a companion object if you want to call it like that instead of calling it on an instance of the class.

enum class ELevel(val label:String){
    Whisper("Whisper"),
    Quiet("Quiet Library");

    companion object {
        fun getLevel(soundValue:Double):ELevel{
           //...
        }
    }

}