Cocoa Programming for OS X: The Big Nerd Ranch Guide

For the More Curious: Creating a Protocol

Creating your own protocol is very simple. Here is a protocol with two methods.

protocol Encryptable {
    init(encryptedData: NSData)
    func encrypt() -> NSData
}

The protocol would typically be defined in a file called Encryptable.swift:

If your protocol is tagged @objc, it is possible to add optional methods.

@objc protocol Encryptable {
    init(encryptedData: NSData)
    func encrypt() -> NSData

    optional func schemeName() -> String
}

In this example, encryptData(_:) and decryptData(_:) are required; schemeName is optional.

If you wanted to make a class conform to both the Encryptable protocol and the NSCoding protocol, the class would begin like this:

class SerializableObject: NSCoding, ...