Singleton with argument in Kotlin

Question

The Kotlin reference says that I can create a singleton using the object keyword like so:

object DataProviderManager {
  fun registerDataProvider(pr         


        

Answer 1

With most of the existing answers it's possible to access the class members without having initialized the singleton first. Here's a thread-safe sample that ensures that a single instance is created before accessing any of its members.

class MySingleton private constructor(private val param: String) {

    companion object {
        @Volatile
        private var INSTANCE: MySingleton? = null

        @Synchronized
        fun getInstance(param: String): MySingleton = INSTANCE ?: MySingleton(param).also { INSTANCE = it }
    }

    fun printParam() {
        print("Param: $param")    
    }
}

Usage:

MySingleton.getInstance("something").printParam()