정의

public protocol Identifiable<ID> {
    associatedtype ID : Hashable
    var id: Self.ID { get }
}

@available(SwiftStdlib 5.1, *)
extension Identifiable where Self: AnyObject {
  public var id: ObjectIdentifier {
    return ObjectIdentifier(self)
  }
}

@available(SwiftStdlib 5.1, *)
extension Identifiable where Self: AnyObject {
	  public var id: ObjectIdentifier {
		    return ObjectIdentifier(self)
	  }
}