Swift - throw error if the element doesn't exist in the array

Question

I've two arrays of int, with 3 elements each. I'm trying to throw an error if the int number I received with func doesn't exist in the arrays

func switch(a: Int, b: Int) throws -> Void {

   if a < 0 || b < 0 || a > arrayA.count || b > arrayB.count {
 
       throw SwitchError.error
}

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I'm trying to use count to do this, but always return the error that numbers don't exist in the array even though they are there... is there another way to achieve this?

class SoccerPlayer {                   
    let name: String
    let number: Int
    init(name: String, number: Int) {
        self.name = name
        self.number = number
    }
}

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class Team {
    var nameTeam: String
    var arrayA: [SoccerPlayer] = []
    var arrayB: [SoccerPlayer] = []
    init(nameTeam: String, arrayA: [SoccerPlayer], arrayB: [SoccerPlayer]) {
        self.nameTeam = nameTeam
        self.arrayA = arrayA
        self.arrayB = arrayB
    }
    func switch(a: Int, b: Int) throws -> Void {
        if a < 0 || b < 0 || a > arrayA.count || b > arrayB.count {
            throw SwitchError.error
        } 
    }
}

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