code from lesson in object oriented programming not working–swift

struct Point {
    let x: Int          
    let y: Int

    init(x: Int, y: Int) {
        self.x = x
        self.y = y

    }/// Returns the surrounding points in range of
    /// the current point.
    func points(inRange range: Int = 1) -> [Point] {
        var results = [Point]()

        let lowerBoundOfXRange = x - range
        let upperBoundOfXRange = x + range

        let lowerBoundOfYRange = y - range
        let upperBoundOfYRange = y + range

        for xCoordinate in lowerBoundOfXRange...upperBoundOfXRange {
            for yCoordinate in lowerBoundOfYRange...upperBoundOfYRange {
                let coordinatePoint = Point(x: xCoordinate, y: yCoordinate)
                results.append(coordinatePoint)
            }
        }
        print(results)
        return results
    }
}

let coordinatePoint = Point(x: 0, y: 0)  //This creates an instance of the struct.

class Enemy {
    var life: Int = 2
    let position: Point

    init(x: Int, y: Int) {
        self.position = Point(x: x, y: y)
    }
    func decreaseLife(by factor: Int) {
        life -= factor
    }
}

class Tower {
    let position: Point
    var range: Int = 1
    var strength: Int = 1

    init(x: Int, y: Int) {
        self.position = Point(x: x, y: y)
    }
    func fire(at enemy: Enemy) {
        if isInRange(of: enemy) {
            enemy.decreaseLife(by: strength)
            print("Gotcha")
        } else {
            print("Darn! Out of range")
        }
        }
    }

    func isInRange(of enemy: Enemy) -> Bool {
        let availablePositions = position.points(inRange: range)

        for point in availablePositions {
            if point.x == enemy.position.x && point.y == enemy.position.y {
                return true
            }
        }

        return false
    }

let tower = Tower(x: 0, y: 0)
let enemy = Enemy(x: 1, y: 1)

tower.fire(at: enemy)