Protocol extensions in Swift

ProtocolExtensions.swift

enum Access {
  case create
  case read
  case write
  case delete
}

protocol PFile {
  func open(access: Access)
  func close()
}

protocol PReadableFile: PFile {
  func openForReading()
  func readText() -> String
  func get() -> String
}

extension PReadableFile {
  func openForReading() {
    open(access: .read)
  }

  func readText() -> String {
    var string: String = ""
    // ...
    return string
  }

  func get() -> String {
    openForReading()
    let string = readText()
    close()
    return string
  }
}

protocol PWritableFile: PFile {
  func openForWriting()
  func write(text: String)
  func set(text: String)
}

extension PWritableFile {
  func openForWriting() {
    open(access: .write)
  }

  func write(text: String) {
    // ...
  }

  func set(text: String) {
    openForWriting()
    write(text: text)
    close()
  }
}

class File: PFile {
  func open(access: Access) {
    // ...
  }

  func close() {
    // ...
  }
}

class MyFile: File, PReadableFile, PWritableFile {
  // This file has all functions
  // Nothing needs to be implemented here
}