Creating enums with specific values/stored properties

Question

I have a

CompassDirection

enum that I normally define in Java like so:

enum CompassDirection {

    N(0, 1), S(0, -1), E(1, 0), W(-1, 0), NE(1, 1), NW(-1, 1), SE(1, -1), SW(-1, -1)

    ...

Where the constructor expects

alterX

and

alterY

integer properties, stores them, and uses them in an

alter(Position position)

method like so:

public Position alter(Position pos) {

    return new Position(pos.x + this.alterX, pos.y + this.alterY);

}

My goal is to accomplish something similar in Swift. I can easily add an 8-case

switch

statement in my

alter()

method but this tends to add a lot more code and confusion.

This is what I tried in Swift:

enum CompassDirection {

    case N(0, 1), S(0, -1), E(1, 0), W(-1, 0), NE(1, 1), NW(-1, 1), SE(1, -1), SW(-1, -1)



    private let xAlter : Int

    private let yAlter : Int



    private init(_ xAlter: Int, _ yAlter: Int) {

        self.xAlter = xAlter

        self.yAlter = yAlter

    }



    func alter(position: XYPosition) -> XYPosition {

        return XYPosition(x: position.x + self.xAlter, y: position.y + self.yAlter)

    }

}

But Swift does not support stored properties in enums.

What is the most readable/Swifty solution for converting the above Java enum to a Swift enum?

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Answer 1

Swift does not support stored properties in enums

You could make xAlter and yAlter computed properties. Here's a highly simplified example (only two cardinal directions):

enum CompassDirection {
    case n
    case s
    var alterX : Int {
        switch self {
        case .n: return 0
        case .s: return 0
        }
    }
    var alterY : Int {
        switch self {
        case .n: return 1
        case .s: return -1
        }
    }
}

Now you can add a method referring to self.alterX and self.alterY, exactly as you desire.

Creating enums with specific values/stored properties

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