Protocols in iOS Object-Oriented Programming

For those who’re new to coding and diving into the world of Swift, some of the thrilling and versatile ideas you’ll encounter is protocols. Protocols are a elementary constructing block of Swift’s object-oriented programming (OOP) mannequin and will help you write cleaner, extra modular, and extra reusable code.

On this article, you’ll discover the facility of protocols and methods to use them to create versatile, adaptable, and sturdy Swift apps. By the top, you’ll have a strong understanding of protocols and be able to put them into apply in your individual tasks. It’s time to get began!

What Are Protocols?

In Swift, a protocol is a blueprint that defines a set of properties, strategies, and different necessities. Lessons, structs, and enums can then “conform” to a protocol, which implies they need to implement the protocol’s necessities.

Protocols are like a contract – they specify what a conforming sort should present however don’t truly implement any of that performance themselves. This separation of interface and implementation is without doubt one of the key advantages of protocols.

Right here’s a easy instance of a protocol in Swift:

import Basis

protocol Nameable {
    var identify: String { get set }
    func introduce()
}

struct Particular person: Nameable {
    var identify: String
    
    func introduce() {
        print("Good day, my identify is (identify).")
    }
}

let tom = Particular person(identify: "Tom")
tom.introduce() // Prints "Good day, my identify is Tom."

On this instance, you outline a Nameable protocol that requires a identify property, with each getter and setter, and an introduce technique. You then create a Particular person struct that conforms to the Nameable protocol by implementing the required properties and strategies.

By utilizing a protocol, you’ve created a generic, reusable blueprint for any sort that must be “nameable.” This makes your code extra modular, versatile, and simpler to take care of.

Protocols and Inheritance

One highly effective function of protocols in Swift is their capability to work seamlessly with inheritance. When a category inherits from one other class, it mechanically inherits the entire properties and strategies of the superclass. However what if you wish to add extra necessities to a subclass?

That is the place protocols come in useful. Check out an instance:

  
import Basis

protocol Car {
    var make: String { get }
    var mannequin: String { get }
    func drive()
}

class Automobile: Car {
    let make: String
    let mannequin: String
    
    init(make: String, mannequin: String) {
        self.make = make
        self.mannequin = mannequin
    }
    
    func drive() {
        print("Driving the (make) (mannequin).")
    }
}

class ElectricCar: Automobile, Chargeable {
    func cost() {
        print("Charging the (make) (mannequin).")
    }
}

protocol Chargeable {
    func cost()
}

On this instance, you’ve a Car protocol that defines the fundamental properties and strategies of a car. The Automobile  class conforms to the Car protocol and gives the required implementations.

You then create a brand new ElectricCar  class that inherits from Automobile  and in addition conforms to a brand new Charcheable protocol. This allows you to add the cost()  technique to the ElectricCar class with out modifying the Automobile  class.

By combining inheritance and protocols, you’ve created a versatile and extensible class hierarchy that may simply accommodate new necessities and behaviors.

Placing it Into Follow

Now that you just perceive protocols, it’s time to place them into apply with a pattern app. You’ll create a primary purchasing cart system that demonstrates the facility of protocols.

Open up a brand new Apple Playground and get began! For those who don’t have Apple Playgrounds, you possibly can obtain it right here: https://developer.apple.com/swift-playgrounds/ 

import Basis

protocol Merchandise {
  var identify: String { get set }
  var value: Double { get set }
}

// Bodily Merchandise Struct (conforms to Merchandise)
struct PhysicalItem: Merchandise {
  var identify: String
  var value: Double
  let weightInGrams: Int
}

// Digital Merchandise Struct (conforms to Merchandise)
struct DigitalItem: Merchandise {
  var identify: String
  var value: Double
  let downloadSize: String
}

// ShoppingCart Protocol
protocol ShoppingCart {
  var gadgets: [Item] { get set }
  mutating func addItem(_ merchandise: Merchandise)
  func calculateTotalPrice() -> Double
}


struct BasicCart: ShoppingCart {

  var gadgets: [Item] = []

mutating func addItem(_ merchandise: Merchandise) { 
    gadgets.append(merchandise)
  }

  func calculateTotalPrice() -> Double {
    var whole = 0.0
    for merchandise in gadgets {
      whole += merchandise.value
    }
    return whole
  }
}

// Utilization Instance
var cart = BasicCart()

let milk = PhysicalItem(identify: "Milk", value: 2.99, weightInGrams: 946)
let e-book = DigitalItem(identify: "Swift Programming Information", value: 9.99, downloadSize: "10MB")

cart.addItem(milk)
cart.addItem(e-book)

let totalPrice = cart.calculateTotalPrice()
print("Whole value: $(totalPrice)") // Prints "Whole value: $12.98"

This instance demonstrates methods to create a primary purchasing cart system in Swift utilizing protocols and structs. Right here’s a breakdown of the code:

Defining the Merchandise Protocol:

You begin by defining a protocol named Merchandise. This protocol acts as a blueprint for any merchandise that may be added to the purchasing cart. It specifies two properties that each one gadgets should have: identify, a string, and value, a double.

Creating Merchandise Structs:

Subsequent, you create two structs, PhysicalItem and DigitalItem, which conform to the Merchandise protocol. PhysicalItem represents a bodily product with an extra property, weightInGrams. DigitalItem represents a digital product with a downloadSize property. Each structs inherit the identify and value properties from the Merchandise protocol.

Designing the ShoppingCart Protocol:

The ShoppingCart protocol outlines the functionalities wanted to handle a group of things within the cart. It defines three properties and strategies:

• var gadgets: [Item] { get set }: This property shops an array of Merchandiseobjects, representing the gadgets within the cart.
• mutating func addItem(_ merchandise: Merchandise): This technique permits including an merchandise to the cart. The mutating key phrase signifies that this technique modifies the cart’s state by including an merchandise.
• func calculateTotalPrice() -> Double: This technique calculates the overall value of all gadgets within the cart based mostly on their particular person costs.

Implementing the BasicCart Struct:

The BasicCart struct implements the ShoppingCart protocol, offering the concrete performance for managing the cart.

• var gadgets: [Item] = []: This initializes an empty array to retailer the gadgets added to the cart.
• mutating func addItem(_ merchandise: Merchandise): This perform appends the offered merchandise to the gadgets array, successfully including it to the cart.
• func calculateTotalPrice() -> Double: This perform iterates via the gadgets array, accumulates the costs of all gadgets, and returns the overall value.

Utilization Instance:

The code demonstrates methods to use the BasicCart struct in apply. You first create a BasicCart occasion referred to as cart. Then, you create two merchandise objects: milk, a PhysicalItem, and e-book, a DigitalItem. You add each gadgets to the cart utilizing the addItem technique. Lastly, you name the calculateTotalPrice technique to get the overall value of all gadgets within the cart and print it to the console.