attachments.swift

enum Attachment {
  case text(info: Text)
  case sticker(info: Stricker)
  
  // common property between text and sticker.
  var position: CGPoint {
    switch self {
      case .text(let info):
        return info.position
      case .sticker(let info): 
        return info.position
    }
  }
}

let aText = Text(content: "Hello World", font: UIFont.systemFont(ofSize: 18), position: .zero)
let aSticker = Stricker(fileURL: URL(string: "http://www.google.com/logo.png")!, position: .init(x: 100, y: 100), scale: 2)
let attachments: [Attachment] = [.text(info: aText), .sticker(info: aSticker)]

// print positions.
for attachment in attachments {
  print(attachment.position)
}