SwiftData @Model object warning: Cannot expand accessors on variable declared with 'let'; this is an error in the Swift 6 language mode

Question

Updated Xcode this morning and my SwiftData models are riddled with warnings about how this will be an error in Swift 6.

Cannot expand accessors on variable declared with 'let'; this is an error in the Swift 6 language mode

An example:

@Model
class Expense {
    let id: UUID // warning here
    var cashflow: Int
    let isPermanent: Bool // warning here
    var name: String
    
    var asset: Asset?
    var liability: Liability?
    
    var player: Player?
    var profession: Profession?
    
    init(name: String, cashflow: Int, isPermanent: Bool) {
        self.id = UUID()
        self.cashflow = cashflow
        self.isPermanent = isPermanent
        self.name = name
    }   
    
}

I can make the warnings go away by changing them from let to var, but what do I do if I want those values to actually be unchangable? I don't want to be able to change the id of the object after it is init'd, so declaring it as a var feels really wrong.

Answer 1

You can use the private access modifier to control who can write to the property

private(set) var id: UUID
var cashflow: Int
private(set) var isPermanent: Bool 
var name: String

Then you only need to be careful with methods in the same class so you don't change the values there.