Decodable enum with associated values

DecodableEnumAssociatedValues.swift

// 
//  Original idea's author is Donny Wals.
//  https://twitter.com/DonnyWals/status/1363840790322102275
//
//  Example modified by Maris Lagzdins on 22/02/2021.
//

import Foundation

// Decodable enum with associated values.
enum Target: Decodable {
    case settings
    case webview(url: URL)
    
    enum CodingKeys: CodingKey {
        // Provide all possible keys from the JSON, which we need to access.
        case target
        case url
    }
    
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        let target = try container.decode(String.self, forKey: .target)
        
        switch target {
        case "settings":
            self = .settings
        case "webview":
            // If the `target` is `webview`, then also decode the `url` key as an URL object.
            let url = try container.decode(URL.self, forKey: .url)
            self = .webview(url: url)
        default:
            // JSON contains unexpected `target` key value, throw error.
            let context = DecodingError.Context(codingPath: decoder.codingPath, 
                                                debugDescription: "Unexpected target: \(target)")
            throw DecodingError.dataCorrupted(context)
        }
    }
}

// ----- EXAMPLE -----

let data = """
[
    {
        "target": "settings"
    }, 
    {
        "target": "webview",
        "url": "https://www.apple.com"
    }
]
""".data(using: .utf8)!

let targets: [Target] = try! JSONDecoder().decode([Target].self, from: data)
print(targets)

for target in targets {
    switch target {
    case .settings:
        print("Navigate to settings")
    case .webview(let url):
        print("Navigate to webview and open the `\(url)`")
    }
}

/* OUTPUT:
 [Page_Contents.Target.settings, Page_Contents.Target.webview(url: https://www.google.com)]
 Navigate to settings
 Navigate to webview and open the `https://www.google.com`
 */