Swift中的自定义类集群 [英] Custom class clusters in Swift

问题描述

这是一个相对常见的设计模式：

This is a relatively common design pattern:

http：// stackoverflow.com/a/17015041/743957

它允许您从您的 init返回一个子类电话。

我试图找出使用Swift实现同样事情的最佳方法。

I'm trying to figure out the best method of achieving the same thing using Swift.

我知道很有可能有一个更好的方法来实现与Swift相同的事情。但是，我的课程将由现有的Obj-C库进行初始化，我无法控制。所以它需要这样工作，可以从Obj-C调用。

I do know that it is very likely that there is a better method of achieving the same thing with Swift. However, my class is going to be initialized by an existing Obj-C library which I don't have control over. So it does need to work this way and be callable from Obj-C.

任何指针都将非常感谢。

Any pointers would be very much appreciated.

推荐答案

我不相信Swift可以直接支持这种模式，因为初始化程序不会像在Objective C中返回一个值 - 所以你没有机会返回一个替代对象实例。

I don't believe that this pattern can be directly supported in Swift, because initialisers do not return a value as they do in Objective C - so you do not get an opportunity to return an alternate object instance.

您可以使用类型方法作为对象工厂 - 一个相当有创意的示例是 -

You can use a type method as an object factory - a fairly contrived example is -

class Vehicle
{
    var wheels: Int? {
      get {
        return nil
      }
    }

    class func vehicleFactory(wheels:Int) -> Vehicle
    {
        var retVal:Vehicle

        if (wheels == 4) {
            retVal=Car()
        }
        else if (wheels == 18) {
            retVal=Truck()
        }
        else {
            retVal=Vehicle()
        }

        return retVal
    }

}

class Car:Vehicle
{
    override var wheels: Int {
      get {
       return 4
      }
    }
}

class Truck:Vehicle
{
    override var wheels: Int {
      get {
          return 18
       }
     }
}

main.swift

main.swift

let c=Vehicle.vehicleFactory(4)     // c is a Car

println(c.wheels)                   // outputs 4

let t=Vehicle.vehicleFactory(18)    // t is a truck

println(t.wheels)                   // outputs 18

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