DecodingCodable.md

Decoding Codable

Ellen Mey - @el_is_for_ellen - from Detroit Labs

What JSON Parsing looked like pre Swift 4

• Huge conditional binding statements.
• Even on structs with small numbers, there were tons of lines of code just to bind, map, encode, and decode.

What it looks like in Swift 4 with Codable

• The whole decoding process takes place on basically one line of code.
• Encoding works pretty much the same way.
• Magic
  • Codable automatically handles your intialization and mapping.

Customizing it to your needs

• Custom Coding Keys
  • Create an enum that conforms to String and CodingKey
  • Create cases for all the keys, and then simply override the default value of the ones where the key on the backend differs from the case name.
• Containers
  • Keyed (like dictionaries) and unkeyed (like arrays) containers
  • Mutable
  • Containers allow us to manipulate data in between JSON and encoding/decoding.
  • Overriding any encoding means you have to then handle all the values.
• Pro tip: If your type will only ever be encoded or decoded, conform to just Encodable or Decodable rather than both, to save you time and effort and overhead.

Ways to deal with less than perfect JSON structures

• keyDecodingStrategy

  • Decoders (or maybe just JSONDecoder) have a keyDecodingStrategy property which will allow you assign things like .convertFromSnakeCase for common decoding scenarios.

• Other things of note:

  • PropertyListEncoder
  • Create a custom encoder
  • dateDecodingStrategy is helpful but currently quite limited
  • Utilizing Codable with other frameworks like RxSwift

• Slides available at here.