Initialization

In Swift, initializers are special methods that can be called to create a new instance of a particular type. They're akin to "constructors" in other programming languages. Initializers prepare the new instance of a class, structure, or enumeration for use, which involves setting an initial value for each stored property and performing any other necessary setup.

Default Initializers:

Swift provides a default initializer for any structure or class that provides default values for all of its properties and does not provide at least one initializer itself.

class ShoppingItem {
   var name: String = ""
   var quantity: Int = 0
}
let item = ShoppingItem() // name is "" and quantity is 0

Memberwise Initializers for Structure Types:

Swift provides a memberwise initializer by default for structures. This initializer is not available for class types.

struct Point {
   var x: Double
   var y: Double
}
let point = Point(x: 0.0, y: 0.0)

Custom Initializers:

You can provide a custom initializer that requires specific information when you create an instance of a class or struct.

class Animal {
   var name: String
   
   // Custom initializer
   init(name: String) {
       self.name = name
   }
}
let aDog = Animal(name: "Rex")

Failable Initializers:

Failable initializers are used for cases where invalid conditions may cause the initialization to fail. These initializers return an optional value.

struct Item {
   var name: String
   var price: Double
   
   // Failable initializer
   init?(name: String, price: Double) {
       if name.isEmpty || price <= 0 {
           return nil
       }
       self.name = name
       self.price = price
   }
}
if let validItem = Item(name: "Vase", price: 42) {
   print(validItem.price) // Prints: 42.0
}
if let invalidItem = Item(name: "", price: 42) {
   // This won't execute because the initializer will return nil
   print(invalidItem.price)
}

Initializer Delegation for Value Types (Structures):

struct Size {
   var width: Double, height: Double
   init(width: Double, height: Double) {
       self.width = width
       self.height = height
   }
   // Initializer Delegation
   init(side: Double) {
       self.init(width: side, height: side)
   }
}
let someSize = Size(side: 50) // width and height will be 50

Class Inheritance and Initialization:

In classes, designated initializers are primary initializers that initialize all properties introduced by the class and call a superclass initializer to continue initialization up the chain.

class Vehicle {
   var numberOfWheels: Int
   
   init(wheels: Int) {
       self.numberOfWheels = wheels
   }
}
class Bicycle: Vehicle {
   var hasBasket: Bool
   init(hasBasket: Bool) {
       self.hasBasket = hasBasket
       super.init(wheels: 2) // Calling a designated initializer from the superclass
   }
}
let bike = Bicycle(hasBasket: true)

These examples showcase various ways initializers can be used in Swift, depending on the requirements of your classes and structures.