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iOS

Posted by Sebastian Nitu
Sebastian Nitu
8,616 Points

Creating a Data Model - Struct vs Class

Hello!

I've just started working on my own app, a calories counter for salads. While the app is not that feature rich, I am having a hard time deciding if I should model a class Vegetables and then subclass each vegetable like Tomato, Cucumber etc from it or if I should go ahead and use a Struct and not use iheritance at all given the fact that all onjects will have the same member values: Name, Color, Vitamins, Calories...

I do not know Core Data nor Ntwroking and remote Databases for now I just want to hardocde everything in the App.

Any ideas / suggestions?

3 Answers

Anthony Boutinov
Anthony Boutinov
13,844 Points
Anthony Boutinov
Anthony Boutinov
13,844 Points

The question is Do you really need to create subclasses for Tomato, Cucumber etc. Maybe Vegetable is enough here.

Maybe even something like this:

import UIKit

struct Vegetable {
    let name: Vegetable.Name
    let color: UIColor
    let vitamins: [Vitamin]

    enum Name: String, CustomStringConvertible {
        case tomato
        case cucumber
        case broadBean

        var description: String {
            switch self {
            case .broadBean:
                return "broad bean"
            default:
                return self.rawValue
            }
        }
    }
}

enum Vitamin: String {
    case a
    case b
    //...
}

With enums the compiler will be able to prevent any typos before running the code. And we can ensure that if we need an image, we can simply do this:

extension Vegetable {
   var image: UIImage {
      return UIImage(named: self.name.rawValue)!
      /* We can force unwrap this because it will only crash
        in case there is no image file corresponding
        to Vegetable.Name enum raw string value. */
   }
}
Anthony Boutinov
Anthony Boutinov
13,844 Points

✝ As of Swift 3, enum cases should be written with first letter being in lowercase.

If you have any questions about the code, just ask =)

Anthony Boutinov
Anthony Boutinov
13,844 Points
Anthony Boutinov
Anthony Boutinov
13,844 Points

As for deciding between using class or struct, structs are usually used to represent data, and classes to represent things that perform actions.

UIViewController is a class because it 1) heavily relies on class hierarchy and 2) has lots of methods that are used to perform actions.

CGPoint is a struct because the only thing it really needs to do is to hold data. It only has two methods, one of which, for example, is to make it possible to check two CGPoints for equality.

Sebastian Nitu
Sebastian Nitu
8,616 Points
Sebastian Nitu
Sebastian Nitu
8,616 Points

Thank you very much for the clarification!