Running a function on an array of structs in Swift UI

Question

I'm trying to build a dice roller where I can add dice to an array, then roll each dice with a random number across the array (so each die has a different number). My current Dice struct is here:

struct Dice: Identifiable, Hashable {
    var id = UUID()
    var displayValue: String
    var initialValue: Int
    var endingValue: Int

    mutating func roll() {
        let randomInt = Int.random(in: initialValue..<endingValue)
        displayValue = "\(randomInt)"
        print("Initial: \(initialValue), EndingValue: \(endingValue), Display: \(displayValue)")
    }
}

and in the main view I have an array of : @State var viewArray: [Dice] = []

I have a SwiftUI button that "rolls" the dice:

Button(action: rollButtonPressed, label: { Text("Roll Dice") })

That triggers this function (where I have my error):

func rollButtonPressed() {
    for dice in viewArray {
        dice.roll()
    }
}

The issue I'm running into is that on the line with dice.roll it throws an error of Cannot use mutating member on immutable value: dice is a let constant

I'm not sure how to fix this, my assumption is that I need to create a loop that triggers the roll() function of each Dice struct to randomize the number they will display, but only trigger once. What should I be looking to fix?

pawello2222 · Accepted Answer · 2020-09-19 18:34:59Z

1

This is because dice need to refer to your original struct and not a copy.

Try replacing:

func rollButtonPressed() {
    for dice in viewArray {
        dice.roll()
    }
}

with:

func rollButtonPressed() {
    for index in viewArray.indices {
        viewArray[index].roll()
    }
}

edited Sep 19, 2020 at 18:34

answered Aug 7, 2020 at 21:22

pawello2222

55.6k23 gold badges184 silver badges240 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Frank Foster Over a year ago

OMG thank you! That was the answer. Works like a charm!

Collectives™ on Stack Overflow

Running a function on an array of structs in Swift UI

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related