class Counter { var count = 0 func increment() { count = count+1 // swift 3.0之前是 count++ } func incrementBy(amount: Int) { count += amount } func reset() { count = 0 } } // 初始计数值是0 let counter = Counter() // 计数值现在是1 counter.increment() // 计数值现在是6 counter.incrementBy(amount:5) //swift 3.0之前是 counter.incrementBy(5) print(counter.count) // 计数值现在是0 counter.reset() print(counter.count)