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Start your free trialJonathan Mazala
9,860 PointsWondering how to solve unwrapping compiler error in swift 4
I'm seeing value of optional type 'Library.LibraryCodingKeys' not unwrapped; did you mean to use '!' or '?'?
I believe my code is the same as in the teacher's example but it's hard to tell exactly because there's no download link
1 Answer
Hao Wu
12,514 PointsHi, I have attached my code and hope it will help you.
import Foundation
let json = """
{
"languages": {
"python": {
"designer": [
"Guido van Rossum"
],
"released": "20 February 1991"
},
"java": {
"designer": [
"James Gosling"
],
"released": "May 23, 1995"
},
"swift": {
"designer": [
"Chris Lattner",
"Apple Inc"
],
"released": "June 2, 2014"
},
"ruby": {
"designer": [
"Yukihiro Matsumoto"
],
"released": "1995"
}
}
}
""".data(using: .utf8)!
struct Language {
let name: String
let designer: [String]
let releaseDate: String
}
struct Library {
let languages: [Language]
struct LibraryCodingKeys: CodingKey {
let stringValue: String
init?(stringValue: String) {
self.stringValue = stringValue
}
var intValue: Int? { return nil }
init?(intValue: Int) { return nil }
static let languages = LibraryCodingKeys(stringValue: "languages")!
}
enum LanguageCodingKeys: String, CodingKey {
case designer
case released
}
}
let decoder = JSONDecoder()
extension Library: Decodable {
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: LibraryCodingKeys.self)
let languagesContainer = try container.nestedContainer(keyedBy: LibraryCodingKeys.self, forKey: .languages)
self.languages = try languagesContainer.allKeys.map { key in
let languageContainer = try languagesContainer.nestedContainer(keyedBy: LanguageCodingKeys.self, forKey: key)
let languageName = key.stringValue
let designer = try languageContainer.decode([String].self, forKey: .designer)
let releaseDate = try languageContainer.decode(String.self, forKey: .released)
return Language(name: languageName, designer: designer, releaseDate: releaseDate)
}
}
}
let library = try! decoder.decode(Library.self, from: json)
for language in library.languages {
print(language.name)
}
Xavier D
Courses Plus Student 5,840 PointsXavier D
Courses Plus Student 5,840 PointsTanx! Proper use of indentations increases readability!
XD