Example of key difference between Classes and Structs in Swift

ClassesAndStructs.swift

  
import UIKit

  // Key Idea: Classes are Reference types and Structs are Value types!
  class Runner {
        
    var type: String
    var level: Int
    var pro: Bool
        
    init(type: String, level: Int, pro: Bool) {
        self.type = type
        self.level = level
        self.pro = pro
    }
  }

  // Classes are reference types. After we set copycat = sprinter,
  // copycat and sprinter now point to the same instance of the Runner
  let sprinter = Runner(type: "sprinter", level: 1, pro: false)
  let copycat = sprinter
  
  // Since copycat references the same instance of the Runner object as
  // sprinter does, we are changing the object that copycat and sprinter
  // point to
  copycat.type = "distance"
  print(sprinter.type) // prints 'distance' because the instance that sprinter
                       // has been modified
  
  struct Jogger {
    
    var age: Int
    var fast: Bool
    
    // itializer not required in structs!
  }
  
  let hobbyJogger = Jogger(age: 21, fast: true)
  var copyHobbyJogger = hobbyJogger
  
  copyHobbyJogger.fast = false
  print(hobbyJogger.fast) // prints true because copyHobbyJogger and hobbyJogger don't
                          // refer to the same instance of Runner but rather the value
                          // of the Runner object itself!
  
// Classes offer inheritance. Structs don't have inheritance so they are light weight