class vs struct

Class

• class is reference type.
• class object is created on Heap memory.
• For class member variable can initialised directly.
• class have constructor and destructor methods of all types.
• class can inherit another class.
• class are good for larger or complex object.

Struct

• struct is value type.
• struct object is created on Stack memory.
• For struct member vaiable can not initialised directly.
• struct can't be abstract.
• stucts are good for small and isolated model object.  

Example of class

- created one Student class with name and lname property with init method

class Student{

    var name : String?

    var lname : String?

    init(name : String?,lname : String?) {

        self.name = name

        self.lname = lname

    }

}

- now create one object for Student class called objStudent and print

let objStudent = Student(name: "Pratik", lname: "Lad")

dump(objStudent)

Output :

__lldb_expr_44.Student #0

  ▿ name: Optional("Pratik")

    - some: "Pratik"

  ▿ lname: Optional("Lad")

    - some: "Lad"

- now one more object create and assign older object of Student class

let obj1Student = objStudent

- now change the name of obj1Student object

obj1Student.name = "Bunty"

- now print both object 

dump(objStudent)

Output :

__lldb_expr_44.Student #0

  ▿ name: Optional("Bunty")

    - some: "Bunty"

  ▿ lname: Optional("Lad")

    - some: "Lad"

dump(obj1Student)

Output :

__lldb_expr_44.Student #0

  ▿ name: Optional("Bunty")

    - some: "Bunty"

  ▿ lname: Optional("Lad")

    - some: "Lad"

you can see the objStudent object name also change because class is reference type.

Example of struct

- created one Student struct with name and lname property with init method

struct Student{

    var name : String?

    var lname : String?

    init(name : String?,lname : String?) {

        self.name = name

        self.lname = lname

    }

}

- now create one object for Student struct called objStudent and print

let objStudent = Student(name: "Pratik", lname: "Lad")

dump(objStudent)

Output :

__lldb_expr_44.Student #0

  ▿ name: Optional("Pratik")

    - some: "Pratik"

  ▿ lname: Optional("Lad")

    - some: "Lad"

- now one more object create and assign older object of Student struct

var obj1Student = objStudent

- now change the name of obj1Student object

obj1Student.name = "Bunty"

- now print both object 

dump(objStudent)

Output :

__lldb_expr_44.Student #0

  ▿ name: Optional("Pratik")

    - some: "Bunty"

  ▿ lname: Optional("Lad")

    - some: "Lad"

dump(obj1Student)

Output :

__lldb_expr_44.Student #0

  ▿ name: Optional("Bunty")

    - some: "Bunty"

  ▿ lname: Optional("Lad")

    - some: "Lad"

you can see the objStudent and obj1Student object name not change because struct is value type.

Thanks for reading this article.

Codable with CoreData

Swift define standard approach to data encoding and decoding which combines the Encodable and Decodable protocols that is called Codable.

In this block I illustrated Codable using API parse and store into CoreData.
First you need to create entity called "List" and create attribute(id,user_id,title,body) like below

List Entity

and then create NSManageObject subclass for List entity.
Now create encode and decode method like below

import Foundation

import CoreData

@objc(List)

public class List: NSManagedObject,Codable {

    

    ///From api response key if changed

    enum apiKey: String, CodingKey {

        case id

        case user_id = "userId"

        case title

        case body

    }

    // MARK: - Decodable

    required convenience public init(from decoder: Decoder) throws {

        

        ///Fetch context for codable

        guard let codableContext = CodingUserInfoKey.init(rawValue: "context"),

            let manageObjContext = decoder.userInfo[codableContext] as? NSManagedObjectContext,

            let manageObjList = NSEntityDescription.entity(forEntityName: "List", in: manageObjContext) else {

                fatalError("failed")

        }

        

        self.init(entity: manageObjList, insertInto: manageObjContext)

        

        let container = try decoder.container(keyedBy: apiKey.self)

        self.user_id = try container.decodeIfPresent(Int64.self, forKey: .user_id) ?? 0

        self.id = try container.decodeIfPresent(Int64.self, forKey: .id) ?? 0

        self.title = try container.decodeIfPresent(String.self, forKey: .title)

        self.body = try container.decodeIfPresent(String.self, forKey: .body)

    }

    

    // MARK: - encode

    public func encode(to encoder: Encoder) throws {

        var container = encoder.container(keyedBy: apiKey.self)

        try container.encode(user_id, forKey: .user_id)

        try container.encode(id, forKey: .id)

        try container.encode(title, forKey: .title)

        try container.encode(body, forKey: .body)

    }

}

Now send server request and parse response using Codable and store into CoreData.

///get data from api

    func getListData()  {

        guard let listURL = URL(string: "https://jsonplaceholder.typicode.com/posts/")else {

            return

        }

        URLSession.shared.dataTask(with: listURL){

            (data,response,error) in

            guard let jsonData = data else { return }

            DispatchQueue.main.async {

                self.parseResponse(forData: jsonData)

            }

        }.resume()

    }

    

    ///parse response using decodable and store data 

    func parseResponse(forData jsonData : Data)  {

        do {

            guard let codableContext = CodingUserInfoKey.init(rawValue: "context") else {

                fatalError("Failed context")

            }

            

            let manageObjContext = appDelegate.persistentContainer.viewContext

            let decoder = JSONDecoder()

            decoder.userInfo[codableContext] = manageObjContext

            // Parse JSON data

            _ = try decoder.decode([List].self, from: jsonData)

            ///context save

            try manageObjContext.save()

            UserDefaults.standard.set(true, forKey: "isAllreadyFetch")

            self.fetchLocalData()

        } catch let error {

            print("Error ->\(error.localizedDescription)")

            self.errorMessage(error.localizedDescription)

        }

    }

And fetch data like below 

    ///Local data fetch from core data

    func fetchLocalData()  {

        let manageObjContext = appDelegate.persistentContainer.viewContext

        let fetchRequest = NSFetchRequest<List>(entityName: "List")

        ///Sort by id

        let sortDescriptor = NSSortDescriptor(key: "id", ascending: true)

        fetchRequest.sortDescriptors = [sortDescriptor]

        do {

            self.arrayOfList = try manageObjContext.fetch(fetchRequest)

        } catch let error {

            print(error)

            self.errorMessage(error.localizedDescription)

        }

    }

The sample code for illustrated in this post is available on GitHub. 

Thank you.