struct User {
    let id:Int
    let name:String
    let avatar:String
}

extension User {

    init?(json:[String:Any]) {

        guard
            let id = json["id"] as? Int,
            let name = json["user_fullname"] as? String,
            let avatar = json["user_avatar"] as? String
        else {
            return nil
        }

        self.id = id
        self.name = name
        self.avatar = avatar
    }
}