设计模式 -- 简单工厂模式

//创建一个抽象类，抽象类中包含了参与运算的抽象子类的属性和方法
class Operation {
    private var _numA = 0
    private var _numB = 0
    
    var numA: Int{
        get{
            return _numA
        }
        set{
            _numA = newValue
        }
    }
    var numB: Int {
        get{
            return _numB
        }
        set{
            _numB = newValue
        }
    }
    func getResult() -> Int {
        return 0
    }
}

//创建负责运算的抽象子类
class OperationAdd:Operation {
    override func getResult() -> Int {
        return self.numA + self.numB
    }
}

//创建负责运算的抽象子类
class OperationSub:Operation {
    override func getResult() -> Int {
        return self.numA - self.numB
    }
}

//创建工厂类，根据参入参数，创建对应的抽象子类实例并返回给外界
class OperationFactory{
    static func createOperation(operatr:String) -> Operation{
        var oper:Operation?
        switch operatr {
        case "+":
            oper = OperationAdd.init()
            break
        case "-":
            oper = OperationSub.init()
            break
        default:
            oper = Operation.init()
        }
        return oper!
    }
}


//每次计算不同的算法直接改变参数里的符号（+、-）
var oper = OperationFactory.createOperation(operatr: "-")
oper.numA = 8
oper.numB = 5
let res = oper.getResult()
print(res)