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iOS Error Handling in Swift Error Handling Handling Errors

Posted by Collin Cannavo
Collin Cannavo
2,494 Points

Error Handling: I'm not getting errors in xCode and the preview isn't showing any issues, but it's still not completing

In the editor, you have a struct named Parser whose job is to deconstruct information from the web. The incoming data can be nil, keys may not exist, and values might be nil as well. In this task, complete the body of the parse function. If the data is nil, throw the EmptyDictionary error. If the key "someKey" doesn't exist throw the InvalidKey error. Hint: To get a list of keys in a dictionary you can use the keys property which returns an array. Use the contains method on it to check if the value exists in the array

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

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

    func parse() throws {
        guard let parsedData = data else {
            throw ParserError.EmptyDictionary
        }
        guard parsedData.keys.contains("someKey") else {
            throw ParserError.InvalidKey
        }
    }
}
let data: [String : String?]? = ["someKey": nil]

do {
  let parser = try Parser(data: data).parse()
} catch let error {
    print(error)
}
Jeff McDivitt
Jeff McDivitt
23,970 Points
Jeff McDivitt
Jeff McDivitt
23,970 Points

What is the exact error that you are receiving when you attempt to run?

3 Answers

Jeff McDivitt
Jeff McDivitt
23,970 Points
Jeff McDivitt
Jeff McDivitt
23,970 Points

Hi Collin -

This is how I completed this challenge. You are on the right track you just needed to go a little farther

enum ParserError: Error {
    case emptyDictionary
    case invalidKey
}

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

    func parse() throws {

        guard let data = data else {
            throw ParserError.emptyDictionary
        }

        guard data["somekey"] != nil else {
            throw ParserError.invalidKey


        }
    }
}

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

do {
    let parser = try Parser(data: data)
    try parser.parse()
} catch ParserError.emptyDictionary(let description) {
    print(description)
}
catch ParserError.invalidKey(let description) {
    print(description)
}
Jordan Ward
Jordan Ward
2,395 Points
Jordan Ward
Jordan Ward
2,395 Points

Hey Jeff I dont mean to be rude, and I'm sure your much more advanced than me but doesn't it say "For this task, just use a generic catch block rather than pattern matching on specific errors". in that case shouldn't you just create a do catch block like..

do { let parser = try Parser(data: data) try parser.parse() } catch let error { print(error) }

Collin Cannavo
Collin Cannavo
2,494 Points
Collin Cannavo
Collin Cannavo
2,494 Points

That's the problem. It's not giving me an error. It says "Your code could not be compiled. Please click on "Preview" to view the compiler errors.", but when I click on the Preview button it's blank; it doesn't show any errors.

Jordan Ward
Jordan Ward
2,395 Points
Jordan Ward
Jordan Ward
2,395 Points

Oh never mind thats part 3 lol