Introducing Swift in higher education

[rayx (Huan Xiong)]

@dabrahams

/// The identity of a person
typealias PersonID = Int

struct Person {
  var name: String;
  var address: String;
}

struct SocialNetwork {
  private var storage: [(Person, friends: [PersonID])] = []
  
  mutating func add(_ newMember: Person) -> PersonID {
    storage.append((newMember, []))
    return storage.count - 1
  }
  ...
}

Hi, Dave, I have two questions on the code. They are mostly implementation details.

1. You use the array index as the value of PersonID. I understand that makes it fast to retrieve a Person value by its ID (I suppose that's why you do it this way), but doesn't that makes PersonID value coupled with the storage format? It seems a bit inflexible to me.

2. Is there any reason why you don't put friends in the Person struct? In practice, a Person may have many properties (e.g., tweets, likes, etc.). I think it's natural to put them in the struct?

   That said, if friends is moved to the struct and suppose we would like to implement a method, say, getFriendNames(), for Person, then the method would need to take a closure to translate PersonID to name. This is a minor example why I said value type often required functional programming techniques.

    // Suppose friendIDs is moved to Person struct
    extension Person {
        func getFriendNames(_ idResolver: (PersonID) -> Person) -> [String] {
            return friendIDs.map { idResolver($0).name }
        }
    }