Protocols in iOS Object-Oriented Programming

When you’re new to coding and diving into the world of Swift, one of the vital thrilling and versatile ideas you’ll encounter is protocols. Protocols are a basic constructing block of Swift’s object-oriented programming (OOP) mannequin and may also help you write cleaner, extra modular, and extra reusable code.

On this article, you’ll discover the ability of protocols and learn how to use them to create versatile, adaptable, and sturdy Swift apps. By the top, you’ll have a stable 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 suggests they have 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("Hiya, my identify is (identify).")
    }
}

let tom = Particular person(identify: "Tom")
tom.introduce() // Prints "Hiya, 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.

Through the use of 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 skill to work seamlessly with inheritance. When a category inherits from one other class, it robotically inherits all the properties and strategies of the superclass. However what if you wish to add extra necessities to a subclass?

That is the place protocols turn out to be 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 gotten a Car protocol that defines the essential properties and strategies of a car. The Automobile  class conforms to the Car protocol and offers the required implementations.

You then create a brand new ElectricCar  class that inherits from Automobile  and likewise 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 Observe

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

Open up a brand new Apple Playground and get began! When you don’t have Apple Playgrounds, you’ll be able to obtain it right here: https://developer.apple.com/swift-playgrounds/ 

import Basis

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

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

// Digital Merchandise Struct (conforms to Merchandise)
struct DigitalItem: Merchandise {
  var identify: String
  var worth: 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.worth
    }
    return whole
  }
}

// Utilization Instance
var cart = BasicCart()

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

cart.addItem(milk)
cart.addItem(book)

let totalPrice = cart.calculateTotalPrice()
print("Complete worth: $(totalPrice)") // Prints "Complete worth: $12.98"

This instance demonstrates learn how to create a primary buying 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 buying cart. It specifies two properties that every one gadgets will need to have: identify, a string, and worth, 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 a further property, weightInGrams. DigitalItem represents a digital product with a downloadSize property. Each structs inherit the identify and worth 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 whole worth 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 operate appends the offered merchandise to the gadgets array, successfully including it to the cart.
• func calculateTotalPrice() -> Double: This operate iterates via the gadgets array, accumulates the costs of all gadgets, and returns the whole worth.

Utilization Instance:

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