Custom class clusters in Swift

Question

This is a relatively common design pattern:

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

It allows you to return a subclass from your init calls.

Answer 1

protocol SomeProtocol {
   init(someData: Int)
   func doSomething()
}

class SomeClass: SomeProtocol {

   var instance: SomeProtocol

   init(someData: Int) {
      if someData == 0 {
         instance = SomeOtherClass()
      } else {
         instance = SomethingElseClass()
      }
   }

   func doSomething() {
      instance.doSomething()
   }
}

class SomeOtherClass: SomeProtocol {
   func doSomething() {
      print("something")
   }
}

class SomethingElseClass: SomeProtocol {
   func doSomething() {
     print("something else")
   }
}

Basically you create a protocol that your class cluster inherits from. You then wrap around an instance variable of the same type and choose which implementation to use.

For example, if you were writing an array class that switched between a LinkedList or a raw array then SomeOtherClass and SomethingElseClass might be named LinkedListImplementation or PlainArrayImplementation and you could decide which one to instantiate or switch to based on whatever is more efficient.