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iOS Error Handling in Swift Error Handling Handling Errors

John Wilcox
John Wilcox
4,233 Points
Posted by John Wilcox
John Wilcox
4,233 Points

Unwrapping needed? Where?

The compiler here keeps saying that something needs to be unwrapped.

Can someone please tell me where the error lies in my second guard statement?

Thanks,

Jack Wilcox

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

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

    func parse() throws {

        // if no dictionary
        guard let dictionary = data else {
            throw ParserError.emptyDictionary
        }

        // if no key
        guard data?.keys.contains("someKey") else {
            throw ParserError.invalidKey
        }

    }
}

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

1 Answer

robb
robb
5,167 Points
robb
robb
5,167 Points

You need to assign data?.keys.contains("someKey") to something:

guard let key = data?.keys.contains("someKey") else {
            throw ParserError.invalidKey
}
John Wilcox
John Wilcox
4,233 Points
John Wilcox
John Wilcox
4,233 Points

Hi Robb, but doesn't .contains return a Bool?

Aren't I essentially checking to see if data?.keys.contains("someKey") is true?