day_11.md

Day 11

Saurabh Jamadagni
7th July, 2022

Restricting access to properties and methods in Structs

• Sometimes you just don't want the properties to be able to be tampered openly. Thus access to them needs to be restricted.
  • For example, funds in a bank account struct shouldn't be able to be modified by just anyone.
• The keyword private restricts the access to a property to the methods inside the struct only. No other external methods can access a private property.
• Following are some of the access modifiers in swift
  1. private -> for access within the struct
  2. fileprivate -> for access within the file
  3. public -> for anyone, anywhere
  4. private(set) -> This allows anyone to read the properties, but only the internal methods can write to it.
• Swift cannot generate a memberwise initialiser on its own if any internal property is private.
• Basically declare a custom init whenever you have private properties.

Static properties

• Sometimes you may want a property to be for the struct only and not for its instances.
• We cannot access non-static properties from static members. static ≠> non-static
• Non-static members can read static members. non-static => static
• We can just access the static member using the self keyword. No need to create an instance.

Checkpoint 6

• Create a car struct that includes model, number of seats and current gear.
• add a method to change gears up or down
• don't allow invalid gears. a range of 1 to 10 is fine.

import Cocoa

enum ShiftingErrors: Error {
  case invalidDownShift, invalidUpShift, invalidShiftString
}

struct Car {
  let model: String
  let numberOfSeats: Int
  var currentGear: Int = 0 // car in neutral
  
  mutating func shiftGears(shift: String) throws {
    switch shift {
    case "up":
      if currentGear < 10 {
        currentGear += 1
        print("upshifting, current gear is now \(currentGear)")
      } else {
        throw ShiftingErrors.invalidUpShift
      }
    case "down":
      if currentGear > 0 {
        currentGear -= 1
        print("downshifting, current gear is now \(currentGear)")
      } else {
        throw ShiftingErrors.invalidDownShift
      }
    default:
      throw ShiftingErrors.invalidUpShift
    }
  }
}

do {
  
  var porsche = Car(model: "porsche 911", numberOfSeats: 2, currentGear: 5)
  try porsche.shiftGears(shift: "up")
  try porsche.shiftGears(shift: "down")
  try porsche.shiftGears(shift: "down")
  try porsche.shiftGears(shift: "down")
  try porsche.shiftGears(shift: "down")
  try porsche.shiftGears(shift: "down")
  try porsche.shiftGears(shift: "down")
  try porsche.shiftGears(shift: "down")
  
} catch ShiftingErrors.invalidUpShift {
  print("Already at highest gear")
} catch ShiftingErrors.invalidDownShift {
  print("Already at the lowest gear")
} catch {
  print("Wrong input string")
}

// Output -------------------------------
// upshifting, current gear is now 6
// downshifting, current gear is now 5
// downshifting, current gear is now 4
// downshifting, current gear is now 3
// downshifting, current gear is now 2
// downshifting, current gear is now 1
// downshifting, current gear is now 0
// Already at the lowest gear

Summary

• learned about access modifiers in swift. They can restrict who has access to struct members.
• Static members are members of a struct and not any particular instance. They are common to all instances.
• Had Checkpoint 6.

Thanks for reading! Let's connect on Twitter 👋