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iOS Error Handling in Swift 2.0 Error Handling Handling Errors

Posted by Scott Baumbich
Scott Baumbich
Courses Plus Student 22,129 Points

Handling Errors Coding Challenge

Hello Community,

I'm hung up on this problem and need some assistance. A better explanation of the question with the use of an example would be helpful. Q&A below:

Q) Now that you have good error handling code, let's call the parse method. Remember that since this is a throwing function, you will need to use a do catch block. For this task, just use a generic catch block rather than pattern matching on specific errors. In the catch clause, simply log an error message of your choosing.

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

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

  func parse() throws {

        guard let someData = data else {
            throw ParserError.EmptyDictionary
        }

        guard let someKey = data!["someKey"] else {
            throw ParserError.InvalidKey
        }
  }
}

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

6 Answers

dmnk
dmnk
18,695 Points

Hey, this works:

enum ParserError: ErrorType {
    case EmptyDictionary
    case InvalidKey
}

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

    func parse() throws {
        guard let _ = data else {
            throw ParserError.EmptyDictionary
        }

        guard let _ = data!["someKey"] else {
            throw ParserError.InvalidKey
        }
    }
}

let data: [String : String?]? = ["someKey": nil]

do {
    let parser = try Parser(data: data).parse()
} catch {
    print("Error")
}
Heather Mathewson
Heather Mathewson
10,912 Points
Heather Mathewson
Heather Mathewson
10,912 Points

That worked! Can you explain the use of the _ after both let's up above? While xcode recommended it to me, I wasnt sure why.

dmnk
dmnk
18,695 Points

Xcode recommended it because both parameters will not be used in the following statement. _ is a placeholder parameter name. It indicates that a parameter is expected, but will not be used.

jakesager
jakesager
12,023 Points
jakesager
jakesager
12,023 Points

I know I'm late, but here's what I came up with that works. It doesn't require force unwrapping using the bang operator.

    func parse() throws {
       // unwrapping data into someData, be sure to use someData from now on
        guard let someData = data else {
            throw ParserError.EmptyDictionary
        }
      // if statement to check whether it has the key
        if !someData.keys.contains("someKey") {
            throw ParserError.InvalidKey
        }
    }
}
vicentelee
vicentelee
6,662 Points

this should be best answer

John Hendrix
John Hendrix
21,844 Points
John Hendrix
John Hendrix
21,844 Points

I had capitol letter errors in the above code. This worked for me:

enum ParserError: Error {
  case emptyDictionary
  case invalidKey
}

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

 func parse() throws {
       // unwrapping data into someData, be sure to use someData from now on
        guard let someData = data else {
            throw ParserError.emptyDictionary
        }
      // if statement to check whether it has the key
        if !someData.keys.contains("someKey") {
            throw ParserError.invalidKey
        }
    }
}

let data: [String : String?]? = ["someKey": nil]

do {
    let parser = try Parser(data: data).parse()
} catch {
    print("Error")
}
Heather Mathewson
Heather Mathewson
10,912 Points
Heather Mathewson
Heather Mathewson
10,912 Points

I am also having trouble with this. Did you figure it out?

Scott Baumbich
Scott Baumbich
Courses Plus Student 22,129 Points

Not yet, I've just skipped ahead. If anything changes I'll let you know.

Scott Baumbich
Scott Baumbich
Courses Plus Student 22,129 Points

Not yet, I've just skipped ahead. If anything changes I'll let you know.

james rochabrun
PLUS
james rochabrun
Courses Plus Student 22,726 Points
james rochabrun
james rochabrun
Courses Plus Student 22,726 Points

enum ParserError: Error { case emptyDictionary case invalidKey }

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

func parse() throws {

    guard (data?["someKey"]) != nil  else {
        throw ParserError.invalidKey
    }

    guard (data?.keys) != nil else {
        throw ParserError.emptyDictionary
    }
}

}

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

do { try parser.parse() } catch ParserError.invalidKey { print(ParserError.invalidKey) }