Networkclient.swift

import Foundation

struct BaseURL {
    
    static let baseURL = "https://learnappmaking.com/"
    
}

struct AppAPI {
    
    static let usersListAPI = "ex/users.json"
}

class NetworkClient {
    
    //MARK:- Properties
    
    var defaultSession: URLSession?
    var dataTask: URLSessionDataTask?
    var request: URLRequest?
    
    //MARK:- Initialiser
    
    required init() {
        defaultSession = URLSession(configuration: .default)
    }
    
    //MARK:- Shared Instance
    
    static let shared = NetworkClient()
}

extension NetworkClient {
    
    //MARK:- Custom Accessors
    
    func fetchData(completion:@escaping(_ users:[User]?)->()) {
        
        let url = URL(string: BaseURL.baseURL+AppAPI.usersListAPI)
        
        request = URLRequest(url: url!)
        request?.httpMethod = "GET"
        
        
        dataTask = defaultSession?.dataTask(with: request!) { data, response, error in
            
            guard error == nil && data != nil else {
                return
            }
            
            if let data = data {
                
                let decoder = JSONDecoder()
                
                do {
                    let userResponse = try decoder.decode(UserResponse.self, from: data)
                    completion(userResponse)
                } catch {
                    print("JSON error: \(error.localizedDescription)")
                }
            }
        }
        
        dataTask?.resume()
    }
}

User.swift

//MARK:- User

struct User: Codable {
    let firstName, lastName: String
    let age: Int
    
    enum CodingKeys: String, CodingKey {
        case firstName = "first_name"
        case lastName = "last_name"
        case age
    }
}

typealias UserResponse = [User]