Example of the incompatibility between OO inheritance and protocol oriented Swift

protocol-oo-inheritance-conflict.swift

/*
A silly example demonstrating how object-oriented inhertitance can conflict with protocol oriented Swift
*/

class Animal {
  func respire() { print("Yum, oxygen") }
}

class Wolf: Animal {
  func growl() { print("Grrrr!") }
}

class Dog: Wolf {
  func saySausages() { print("Sausages!") }
}

protocol Reproducible {
  func reproduce(other: Self) -> Self
}

// The extension below will not compile.
// Non of our animals can conform to the Reproducible protocol.
// The Self requirement in the protocol requires that classes must be final (no OO inheritance)
extension Wolf: Reproducible {
  func reproduce(other: Wolf) -> Wolf {
    return Wolf()
  }
}