My attempt to solve 'Checkpoint 6' of #100DaysOfSwiftUI (https://www.hackingwithswift.com/100/swiftui)

100DaysOfSwitfUI - Day 11 - Checkpoint 6.swift

// Bear with me - sure, exceptions, custom initializers, observers, static methods,
// computed properties, etc. are really not all needed to solve the problem, but I
// wanted to try some of the things we learned so far and thereby the code got a bit
// bloated maybe.

struct NonSense: Error {
}

struct Car {
    
    // Okay, I do allow -1 as a valid value ... I read the hyphen as a minus
    // and "-1...10 seems a fair maximum range" made perfect sense to me 😂
    static let minGear = -1
    static let maxGear = 10
    
    let model: String
    let numberOfSeats: Int
    
    // I liked the concept of that `private(set)` - did always want something like
    // this in other languages. But now that I see how it turned out, I'm not so
    // sure - maybe doing the range check using obeservers might have been the better
    // approach?!?
    
    private(set) var currentGear: Int = 0 {
        didSet {
            print("[engine makes some noise and now we are at currentGear=\(currentGear)]")
        }
    }
    
    
    init(model: String, numberOfSeats: Int = 5) throws {
        self.model = model
        
        if numberOfSeats < 1 {
            throw NonSense()
        }

        self.numberOfSeats = numberOfSeats
    }
    
    mutating func gearUp() -> Bool {
        if currentGear >= Self.maxGear {
            print("[what are you trying to do here?]")
            return false
        }
        
        currentGear += 1
        return true
    }
    
    mutating func gearDown() -> Bool {
        if currentGear <= Self.minGear {
            print("[that gear stick will hardly move any further!]")
            return false
        }
        
        currentGear -= 1
        return true
    }

    func gearAsString() -> String {
        
        switch currentGear {
            case -1:
                return "R"
            case 0:
                return "N"
            default:
                return "D"+String(currentGear)
        }
    }
    
    var string: String {
        "I'm a \(model) with \(numberOfSeats) seats and my gear lever in the '\(gearAsString())' position"
    }
    
    static func crash() {
        print("Outch, that went terribly wrong!")
    }
}


do {
    var car: Car
    
    car = try Car(model: "Citroën DS", numberOfSeats: 4)
    print(car.string)
    car.gearDown()
    print(car.string)
    car.gearDown()
    print(car.string)
    car.gearUp()
    print(car.string)
    car.gearUp()
    print(car.string)
    car = try Car(model: "Citroën DS", numberOfSeats: -1)
    print(car.string)

}   catch {
    
    Car.crash()
}

/* OUTPUT:
 
 I'm a Citroën DS with 4 seats and my gear lever in the 'N' position
 [engine makes some noise and now we are at currentGear=-1]
 I'm a Citroën DS with 4 seats and my gear lever in the 'R' position
 [that gear stick will hardly move any further!]
 I'm a Citroën DS with 4 seats and my gear lever in the 'R' position
 [engine makes some noise and now we are at currentGear=0]
 I'm a Citroën DS with 4 seats and my gear lever in the 'N' position
 [engine makes some noise and now we are at currentGear=1]
 I'm a Citroën DS with 4 seats and my gear lever in the 'D1' position
 That went terribly wrong!

 
 */