Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

iOS Error Handling in Swift 2.0 Error Handling Handling Errors

Jack Hancock
Jack Hancock
3,613 Points
Posted by Jack Hancock
Jack Hancock
3,613 Points

Can't seem to figure out how to use the contains method.

I have tried many variations of code to get the ParserError.InvalidKey to throw when "someKey" is non existent. Any tips or help would be great, thanks.

error.swift 
enum ParserError: ErrorType {
  case EmptyDictionary
  case InvalidKey
}

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

  func parse() throws {

  if (data == nil) {
  throw ParserError.EmptyDictionary
    } 
    let value = data?.keys
    if (value.contains("someKey") == false) {
    throw ParserError.InvalidKey
    }
  }
}

let data: [String : String?]? = ["someKey": nil]
let parser = Parser(data: data)

1 Answer

Nathan Tallack
Nathan Tallack
22,160 Points
Nathan Tallack
Nathan Tallack
22,160 Points

You were VERY close.

You need to take care to use optional binding when working with the optional returns of dictionaries. Consider your code below.

enum ParserError: ErrorType {
  case EmptyDictionary
  case InvalidKey
}

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

  func parse() throws {
    if (data == nil) {
      throw ParserError.EmptyDictionary
      } 
    if let value = data?.keys {  // Optional binding here.
      if (value.contains("someKey") == false) {
        throw ParserError.InvalidKey
      }
    }
  }
}

let data: [String : String?]? = ["someKey": nil]
let parser = Parser(data: data)
Jack Hancock
Jack Hancock
3,613 Points
Jack Hancock
Jack Hancock
3,613 Points

Thanks so much! I was stumped on this for a very long time last night, glad to see I was at least close.