Using variable as lower bound for arc4random - explicit type/strideable?

Question

)

I have updated a "Workout Object" to have both a minimum and maximum number of reps.

When I've been hardcoding the lower bound in a playground, I've been using :

let numberOfExercises = Int(arc4random_uniform(4) + 3)

When I try to use variables in a function/with a class object I get an error of "+'is unavailable: Please use explicit type conversions or Strideable methods for mixed-type arithmetics" e.g. here ...

class ExerciseGeneratorObject: Object {
    @objc dynamic var name = ""
    @objc dynamic var minReps = 0
    @objc dynamic var maxReps = 0    

    convenience init(name: String, minReps: Int, maxReps: Int) {
        self.init()
        self.name = name
        self.minReps = minReps
        self.maxReps = maxReps
    }

    func generateExercise() -> WorkoutExercise {
        return WorkoutExercise(
            name: name,
//get error on this line...
            reps: Int(arc4random_uniform(UInt32(maxReps))+minReps)
        )
    }
}

There is an answer here + is unavailable: Please use explicit type conversions or Strideable methods for mixed-type arithmetics but that method is already using so don't see how it's applicable here.

Also here '+' is deprecated: Mixed-type addition is deprecated in Swift 3.1 but again think this is a different problem

Answer 1

'+' is unavailable: Please use explicit type conversions or Strideable methods for mixed-type arithmetics.

Example:

let a: UInt32 = 4
let b = 3

let result = a + b //error

Basically means you can't add mixed-types.

---

In your case when you do arc4random_uniform(UInt32(maxReps)) + minReps, arc4random_uniform() returns a UInt32 which cannot be added to minReps because that's an Int.

Solution:

Update your parenthesis:

let numberOfExercises = Int(arc4random_uniform(UInt32(maxReps))) + minReps

Here Int(arc4random_uniform(UInt32(maxReps))) gives an Int that we can add to the minReps Int.

---

BTW, the following works out-of-the-box:

let numberOfExercises = Int(arc4random_uniform(4) + 3)

Because of Swift's automatic type inference. Basically it just went ahead with UInt32 without bothering you. That is... until you give it explicit mixed types.