//设置计算型属性：其并不真正的存储值，而是每次通过其他值计算得来var subtotal: Double {  //getter:通过total、taxPct计算获得total的值    get {    return total / (taxPct + 1)  }  //setter:更新的是相关的值（比如此处基于newSubtotal来设置total、taxPct的值）  set(newSubtotal) {      //...   }}

//创建一个unamed tupleslet tipAndTotal = (4.00, 25.19)//创建一个named tupleslet tipAndTotalNamed = (tipAmt:4.00, total:25.19)tipAndTotalNamed.tipAmttipAndTotalNamed.total//单行创建tupleslet tipAndTotalNamed:(tipAmt:Double, total:Double) = (4.00, 25.19)

let total = 21.19let taxPct = 0.06let subtotal = total / (taxPct + 1)//这里返回的是元组的类型func calcTipWithTipPct(tipPct:Double) -> (tipAmt:Double, total:Double) {  let tipAmt = subtotal * tipPct  let finalTotal = total + tipAmt  return (tipAmt, finalTotal)}calcTipWithTipPct(0.20)