Scala objects that do not change their internal state

Question

I see a problem with some Scala 2.7.7 code I'm working on, this should not happen if the equivalent was written in Java. Wrong, the code goes, creates a bunch of card players and assigns them to the tables.

class Player(val playerNumber : Int)

class Table (val tableNumber : Int) {
    var players : List[Player]  = List()

    def registerPlayer(player : Player) {
        println("Registering player " + player.playerNumber + " on table " + tableNumber)
        players = player :: players
    }
}

object PlayerRegistrar  {
    def assignPlayersToTables(playSamplesToExecute : Int, playersPerTable:Int) = {
        val numTables = playSamplesToExecute / playersPerTable
        val tables = (1 to numTables).map(new Table(_))
        assert(tables.size == numTables)

        (0 until playSamplesToExecute).foreach {playSample =>
            val tableNumber : Int = playSample % numTables
            tables(tableNumber).registerPlayer(new Player(playSample))
        }
        tables
    }
}

PlayerRegistrar assigns multiple players between tables. First, it determines how many tables you need to split the players between them and create a list of them.

Then, in the second part of the code, a table is issued to which the player should be assigned, pulls this table from the list and registers a new player in this table.

The list of players in the table is var and is overwritten each time registerPlayer () is called. I checked that this works correctly with a simple TestNG test:

@Test def testRegisterPlayer_multiplePlayers() {
    val table = new Table(1)
    (1 to 10).foreach { playerNumber =>
        val player = new Player(playerNumber)
        table.registerPlayer(player)
        assert(table.players.contains(player))
        assert(table.players.length == playerNumber)
    }
}

Then I check the purpose of the table:

  @Test def testAssignPlayerToTables_1table() = {
    val tables = PlayerRegistrar.assignPlayersToTables(10, 10)
    assertEquals(tables.length, 1)
    assertEquals(tables(0).players.length, 10)
}

": < 10 > , : < 0 > ". , , registerPlayer() . .

Answer 1

, assignPlayersToTables Table. , :

val tableNumber : Int = playSample % numTables
println(tables(tableNumber))
tables(tableNumber).registerPlayer(new Player(playSample))

- :

Main$$anon$1$Table@5c73a7ab
Registering player 0 on table 1
Main$$anon$1$Table@21f8c6df
Registering player 1 on table 1
Main$$anon$1$Table@53c86be5
Registering player 2 on table 1

, .

, a Range Scala ( Scala 2.8, ). , , . , , Table, , ( Table) , . , , :

val tables = (1 to numTables).map(new Table(_))
println(tables)

:

RangeM(Main$$anon$1$Table@5492bbba)

, , toList :

val tables = (1 to numTables).map(new Table(_)).toList

Answer 2

val tables = (1 to numTables).map(new Table(_))

, -, - 1 to n RandomAccessSeq.Projection, , , , , .

var tables: Array[Table] = new Array(numTables)
for (i <- 0 to numTables) tables(i) = new Table(i)

, ( ), , , .