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Singleton.kt

/**
 * Simple singleton class with double-check pattern
 */
class Singleton private constructor() {

    private val data: String = "data property value"

    @Volatile
    private var singleton: Singleton? = null

    fun getInstance(): Singleton {
        if (singleton == null) {
            synchronized(this) { 
              if (singleton == null) { 
                singleton = Singleton()
              }
            }
        }

        return singleton!!
    }
}