Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

iOS Error Handling in Swift Error Handling Handling Errors

Sam Belcher
Sam Belcher
3,719 Points

Handling Errors Challenge Swift

Hi, I rewatched the videos a bunch of times but I still don't understand the challenge.

error.swift
enum ParserError: Error {
  case emptyDictionary
  case invalidKey
}

struct Parser {
  var data: [String : String?]?

  func parse() throws {

  }
}

let data: [String : String?]? = ["someKey": nil]
let parser = Parser(data: data)
func parse() throws {
    guard let data = data else { throw ParserError.emptyDictionary }
    guard let key = data["someKey"] else { throw ParserError.invalidKey }
}

First, you need to unwrap the data so that you will know if the has values in it. Then you need to check if someKey has value using guard let or if let statement.

1 Answer

Maria Te
Maria Te
8,520 Points

I agree with that but a more effective way is:

func parse() throws {
    guard let data = data else { throw ParserError.emptyDictionary }
    guard data["someKey"]  != nil else { throw ParserError.invalidKey }
}

See, when I followed your code, Xcode sent a warning saying that making a new constant could be fixed to a more effective answer. So I changed it to this code and everything seemed perfect. Hope that this helps! :-D