How does `key` pointer address remain the same between get/set calls?

[suparngp]

A noob question may be.

Following up on your example:

var identifier: String {
      get {
          return getAssociatedValue(key: "identifier", object: self, initialValue: "Unknown")
      }
      set {
          set(associatedValue: newValue, key: "identifier", object: self)
      }
  }

"identifier" in both get and set should have different memory addresses since they are two different objects. So how is it able to retrieve the previously stored value?