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Thanks, Miki, for your comment. I think your understanding is correct. It will always return the first created instance.

Technically, I think the code should throw an exception if the requested singleton name (parameter) is different from the first originally created.

The example is to demonstrate sometimes we can't just use object keyword, especially you need an additional parameter. Maybe this example is not a good one. :)

Whether it is common or not to give parameters to singleton, I'm not sure, but database creation is pretty common to be used as singleton. See below example. It doesn't have a constructor parameter (although it can). But, it requires passing in context to create database.

abstract class ArticlesDatabase : RoomDatabase() {

    protected abstract val dao: ArticlesDao

    companion object {
        @Volatile
        private lateinit var instance: ArticlesDatabase

        fun getInstance(context: Context): ArticlesDatabase 
        {
            synchronized(this) {
                if (!::instance.isInitialized) {
                    instance = Room.databaseBuilder(
                        context.applicationContext,
                        ArticlesDatabase::class.java,
                        "articles.db")
                        .fallbackToDestructiveMigration()
                        .build()
                }

                return instance
            }
        }
    }
}