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