Archivable

Archivable is a library for functionally encoding and decoding Swift value types, allowing them to stored locally with NSUserDefaults or another NSData cache. The library was heavily inspired by the functional JSON parsing library, Argo.

How do I use it?

Archivable is a protocol that defines two methods, encode(encoder: Encoder) and decode(decoder: Decoder) -> Decoded<Self>. The first allows custom types to be encoded and stored as serialized NSData, while the second allows those types to then be failably decoded and initialized from NSData.

Example

In the following example, we define a simple model, Person, which contains two stored properties: name of type String, and age of type Int. We then extend our Person model to conform to Archivable, providing the two method implementations necessary for encoding and decoding to/from NSData.

import Runes
import Archivable

struct Person {
  let name: String
  let age: Int
}

extension Person: Archivable {
  func encode(encoder: Encoder) {
    encoder.encode(name, forKey: "name")
    encoder.encode(age, forKey: "age")
  }

  static func decode(coder: NSKeyedUnarchiver) -> Decoded<Person> {
    return curry(Person.init)
      <^> decoder.decode("name")
      <*> decoder.decode("age")
  }
}

Now, you can easily encode and store any instance of Person, just as you would with a NSCoding compliant model, but you get all the inherent benefits of immutable value types. 🎉

For example, we can save a Person to NSUserDefaults, then decode again later as needed:

let defaults = NSUserDefaults.standardUserDefaults()
let giles = Person(name: "Giles", age: 21)

// Encode
defaults.setValue(giles, forKey: "dummy")

// Decode
let decodedGiles: Decoded<Person> = defaults.valueForKey("dummy")

// Confirm
if let dummy = decodedGiles.value {
    print(dummy.name) // prints "Giles"
}