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iOS Error Handling in Swift 2.0 Error Handling Handling Errors

Julien Schmitt
Julien Schmitt
2,334 Points

Confused about the statement - Error handling

Hi all,

I'm not sure that I understood well what has to be done in this exercice.

  1. Should I specify a return parameter for the parse function?
  2. "if the data is nil". Which data of what? The constant?
  3. Same question for the "someykey" data.



enum ParserError: ErrorType {
  case EmptyDictionary
  case InvalidKey

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

  func parse() throws {
        guard let data = Parser(data: data) else {
            throw ParserError.EmptyDictionary

        guard let parser = ["someKey": String] else {
            throw ParserError.InvalidKey

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

1 Answer

Tassia Castro
Tassia Castro
iOS Development Techdegree Student 9,170 Points

No, you shouldn’t. What you have to do is only check if the dictionary ‘data’ is nil and if the key “someKey” exists. If it doesn’t, you throw an error.

The ‘data’ that he means is : var data: [String : String?]?

In the exercise a dictionary called data is created with this value: [“someKey”: nil]. So, inside the func parse, you need to check if this dictionary has indeed a key called “someKey”.

In order to check if the dictionary is nil, you can use the guard statement and it would be something like that:

guard let xValue = x else { // x is what you wanna check if it is nil throw an error }

ps: As the dictionary is not nil, the error will not be thrown.

In order to check if the key exists, use the if statement with the methods that are shown in the quiz. Adapt this if (x) with the dictionary of the quiz.

// if x does not contains (“someKey”), throw an error. if !x.keys.contains(“somekey”) { throw an error }

ps: As the dictionary data has indeed a key called ‘someKey’, this error will not be thrown.