How can I access a val from a data class in kotlin?-CodePudding

So I want to access isInBounds

Navigation.kt:

data class Coordinate(val x:Int , val y:Int){

    val isInBounds = x >= 0 && y >= 0

    operator fun plus(other:Coordinate) = Coordinate(x   other.x, y   other.y)

}

But when I try to access it I get an unresolved reference.

Game.kt

private fun move(directionInput: String) = try {
    val direction = Direction.valueOf(directionInput.uppercase())
    val newPosition = direction.updateCoordinate(player.currentPosition)


    

    if (!newPosition.isInBounds){

    }
    else{

    }
} catch (e: Exception){

}

enum class Direction(private val  coordinate: Coordinate){
    NORTH(Coordinate(0 , -1)),     
    EAST(Coordinate(1 , 0)),     
    SOUTH(Coordinate(0 , 1)),     
    WEST(Coordinate(-1 , 0));      
    fun updateCoordinate(playerCoordinate:Coordinate) {         
        coordinate   playerCoordinate     
    } 
}

CodePudding user response：

The mistake is in Direction. Note that you did not specify a return type for updateCoordinate, and you used a block body for it. This means that it implicitly returns Unit. So updateCoordinate calculates coordinate playerCoordinate, discards the result, and returns Unit. This causes newPosition to be Unit, and that is obviously not going to be have an isInBounds property.

Clearly that is not what you want. You should instead declare updateCoordinate with an expression body:

fun updateCoordinate(playerCoordinate:Coordinate) =
    coordinate   playerCoordinate

or if you like block bodies:

fun updateCoordinate(playerCoordinate:Coordinate): Coordinate {
    return coordinate   playerCoordinate
}

This is just my opinion, but I think it is more readable to have updateCoordinate as a method on Coordinate, called moveTowards:

data class Coordinate(val x: Int, val y: Int) {
    operator fun plus(coord: Coordinate) = ...

    fun moveTowards(direction: Direction) =
        this   direction.coordinate // you'd have to make direction.coordinate public
}

CodePudding user response：

Your updateCoordinate function doesn't actually accomplish anything because it calculates something without doing anything with the result, like returning it. Therefore, it implicitly returns Unit, so newPosition is just a reference to Unit.

Change the function to return the new coordinate:

fun updateCoordinate(playerCoordinate: Coordinate): Coordinate {         
    return coordinate   playerCoordinate     
}

I recommend giving this function a better name. The word "update" implies that it is mutating the instance that is passed to it instead of calculating a new one.

Logically, since this function is something that adds something to a coordinate, it would make more sense for legibility and easy reasoning of your code to invert it (swap the receiver and parameter). So I would pull this function out of the enum class and make it a Coordinate extension function.

fun Coordinate.moved(direction: Direction): Coordinate {
    return this   direction.coordinate
}

but you'll have to make the Direction's coordinate property public or internal.