in swift 3, now they give us a new better way to define getter and setter, that’s really nice when you have whole bunch of variables there.

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// example code from the iOS 10 course by Mark Price, highly recommended!
class TipCalc {
  private var _billAmount = 0.0
  private var _tipPercent = 0.0
  private var _tipAmount = 0.0
  private var _totalAmount = 0.0
  //
  var tipAmount: Double {
    return _tipAmount
  }
  // this will be a read-only computed attribute,
  // you can even use dot(.) to access the value
  //
  var billAmount: Double {
    get {
      return _billAmount
    } set {
      _billAmount = newValue
    }
  }
}

the variable newValue inside the setter was default given naming by swift, even it was an instance variable of a struct, check the following example
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struct AlternativeRect {
  var origin = Point()
  var size = Size()
  var center: Point {
    get {
        let centerX = origin.x + (size.width / 2)
        let centerY = origin.y + (size.height / 2)
        return Point(x: centerX, y: centerY)
    } set {
        origin.x = newValue.x - (size.width /2)
        origin.y = newValue.y - (size.height /2)
    }
  }
}