Swift4_JSON_05.swift

import Foundation

let json = """
[
    { "name": "magicien" },
    { },
    { "name": "NoName" }
]
""".data(using: .utf8)!

struct UserInfo: Codable {
    let _name: String?
    var name: String {
        get { return self._name ?? "NoName" }
    }
    
    enum CodingKeys: String, CodingKey {
        case _name = "name"
    }
}

let decoder = JSONDecoder()
do {
    let users = try decoder.decode([UserInfo].self, from: json)
    for user in users {
        print("\(user.name), Default: \(user._name == nil)")
    }
} catch DecodingError.keyNotFound(let key, let context) {
    print("keyNotFound: \(key): \(context)")
} catch {
    print("\(error.localizedDescription)")
}

/*
 magicien, Default: false
 NoName, Default: true
 NoName, Default: false
*/