Question 1

Please consider the following code: (Advanced)

enum BookType {
    case biology
    case physics
    case maths
    case unknown
}
class Book {
    var name:String?
    var type:BookType = .unknown
}
class BookStorage {
        func fetchAllBooks() -> [Book] {
            // return all available books
        }
  }
class BooksManager {
        func physicsBooks() -> [Book] {
            let books = BookStorage().fetchAllBooks()
            // identify the physics book and return those
            let physicsbooks …
            return physicsbooks
        }
}

We want to test cover the function of physicsBooks. Test the logic if it identifies the physics books from different data sets. Redesign this classes to test cover the method.

Accepted Answer

Use dependency injection to redesign the classes and provide data from test methodsprotocol IBookStorage {
func fetchAllBooks()->[Book]
}
class BookStorage: IBookStorage  {
    func fetchAllBooks() -> [Book] {
        // return all available books
    }
}

class BooksManager {
        let bookStorage:IBookStorage
        init(bookStorage:IBookStorage) {
            self.bookStorage = bookStorage
        }
        func physicsBooks() -> [Book] {
            let books = bookStorage.fetchAllBooks()
            // identify the physics book and return those
            let physicsbooks = …
            return physicsbooks
        }
    }
class StubBookStorage: IBookStorage  {
    var books = [Book]()
    init(books:[Book]) {
        self.books = books
    }
    func fetchAllBooks() -> [Book] {
        return books
    }
}
// Test methods
   func testBookManager() {
let books = …  // add stub data you want to test
let bookStorage = StubBookStorage(books: books)
let bookManager = BooksManager(bookStorage: bookStorage)
let physicsBooks = bookManager.physicsBooks()
// test the value physicsBooks array if correct
    }This, along with other Swift basic questions for freshers, is a regular feature in Swift programming interviews, be ready to tackle it with the approach mentioned.

Question 2

Consider a scenario where I have two different system storage which requires IDs in different data types. One system will deal int values only and others in string values only. Create a generic protocol with a single property &ldquo;ids&rdquo; ( holds an array of ids) and a function to add id, that will be used for two systems.

Accepted Answer

Key is to use associated types, which is a powerful way of making protocols generic.protocol Store {
    associatedtype DataType
    var ids: [DataType] { get set}
    mutating func add(id: DataType)
}
extension Store {
    mutating func add(id: DataType) {
        ids.append(id)
    }
}
struct SystemOne: Store {
    var ids = [String]()
}
struct SystemTwo: Store {
    var ids = [Int]()
}
var sysOne = SystemOne()
sysOne.add(id: "One")
sysOne.add(id: "Two")
var sysTwo = SystemTwo()
sysTwo.add(id: 1)
sysTwo.add(id: 2)
print(sysOne.ids)
print(sysTwo.ids)

Question 3

What is the exact difference in the view model in MVVM and controller in MVC? Which pattern is preferable keeping in mind the code unit test coverage?

Accepted Answer

In MVC, controller is coordinated that reads / saves data into the data model and displays data / handles actions in the view.

In MVVM, the view model is a close representation of a view. The view model is bound to the view. Any change in data in the view model, leads to notifiications and view pulls data from the view model and it displays it.

Test covering controllers can be a bit difficult as view is tightly attached to a view i.e View controller will have an instance of a view within it. So it will be difficult to mock the view methods called from the controller.

Test covering in ViewModel is rather easy as it does not contain any reference to a view. Rather it only prepares data for the view only. It is the view that pulls the data from the view model. Also, the view delegates the action to the View model.

One of the most frequently posed Swift iOS interview questions, be ready for this conceptual question.

Question 4

Please look at the code segment below. If we compile it what happens? Explain

class A {
    var name:String
    init(name:String) {
        self.name = name
    }
}
class B:A {
    var id : String
    init(name:String, id : String){
        self.id = id
        super.init(name: name)
    }
    convenience init (id:String) {
        super.init(name: "unknown")
        self.id = id
    }
}

Accepted Answer

The derived class convenience initializers only and call convenience initializer or designated initializer of own class. Ultimately the call chain should have designated initializer at last of the same class.So the correct code is :class A {
    var name:String
    init(name:String) {
        self.name = name
    }
}
class B:A {
    var id : String
    init(name:String, id : String){
        self.id = id
        super.init(name: name)
    }
 convenience init (id:String) {
self.init(name: "unknown", id: id)
    }
}This is a common yet one of the most important Swift coding interview questions and answers for experienced professionals, don't miss this one.

Question 5

In the code below when what will happen if we compile and execute SwiftBasics. test() method. Provide reasons.

  class SwiftBasics {
      static func test() {
        let emp1 = Employee(name: "John", id: 10)
        let emp2 = Employee(name: "John", id: 10)
        print("\(emp1 == emp2)")
    }
}
struct Employee {
    var name:String
    var  id:Int
    init(name:String, id:Int) {
        self.name = name
        self.id = id
    }
}

Accepted Answer

It would provide a compilation error as  emp1 == emp2 cannot be resolved by compiler. It depends if the structs/classes are adapted to the Hashable protocol. The primitive data type like Int, String by default implement the Hashable protocol, show they do not show any error if we compare instances of such data types.The corrected code would be:struct Employee: Hashable {
    var name:String
    var  id:Int
    init(name:String, id:Int) {
        self.name = name
        self.id = id
    }
    var  hashValue: Int { return self.id}
}
The printed result would be true.This is one of the most frequently asked Swift interview questions for freshers and experienced in recent times.

Question 6

Consider the following code snippet

class Transport {
    var type:String
    init(type:String) {
        self.type = type
        print("Transport - \(type)")
    }
}
class Car:Transport {
    var model:String
    init(model:String){
        super.init(type: "Car")
        self.model = model
         self.model = "\(self.model) - type \(self.type)"
        print("\(self.model)")
    }
}
If we try to execute the following what will be the result. Provide reasons
  let car = Car(model:”Maruti”)

Accepted Answer

There will be a compilation error. The derived class Car calls the init method of superclass before its stored property, model gets initialised. Swift does 2 phase initialization, in first phase memory is allocated and all stored properties get initialized starting from the derived classes and then its superclass. Then in the second phase, all customizations of the properties are done, in the init method.The correct code will be :class Car:Transport {
    var model:String
    init(model:String){
        self.model = model
        super.init(type: "Car")
         self.model = "\(self.model) - type \(self.type)"
        print("\(self.model)")
    }
}
The result will be
  Transport - Car
   Maruti  - type CarA staple Swift interview question for senior developer, be prepared to answer this one using your hands-on experience. This is also one of the top interview questions to ask an application developer.

Question 7

What is the use of the dump function? Explain with example.

Accepted Answer

Dump function is used to print the content of the object For eg: class Person {
    let name: String
    let cars: [String]?
    init(name:String, cars: [String]?) {
        self.name = name
        self.cars = cars
    }
}let allPerson = [Person(name: "P1", cars: ["P1_C1", "P1_C2"]), Person(name: "P2", cars: ["P2_C1", "P2_C2"])]dump(allPerson)Output:▿ 2 elements
  ▿ App.Person #0
    - name: "P1"
    ▿ cars: Optional(["P1_C1", "P1_C2"])
      ▿ some: 2 elements
        - "P1_C1"
        - "P1_C2"
  ▿ App.Person #1
    - name: "P2"
    ▿ cars: Optional(["P2_C1", "P2_C2"])
      ▿ some: 2 elements
        - "P2_C1"
        - "P2_C2"
//As seen, dump() outputs the whole class hierarchy, while print() simply outputs the class name.

Question 8

Please look at the code below. If we run method ., what will be the output and why?

class Employee4 {
    var name:String
    var  id:Int
    init(name:String, id:Int) {
        self.name = name
        self.id = id
    }
}
func testAssignment() {
    let emp1 = Employee4(name: "Sam", id: 1)
    let emp2 = Employee4(name: "John", id: 2)
    let emp3 = Employee4(name: "Robert", id: 3)
    var employees = [emp1,emp2]
    let employees2 = employees
    employees[0].name = "Sam Smith"
    employees.append(emp3)
    for emp in employees2 {
        print("name \(emp.name)")
    }
}

Accepted Answer

name Sam Smithname JohnExplanation: employee3 is a struct, and we assign  employees2 = employees separate array in memory is created in the memory.  And when we add emp3 in employees it is not reflected in employees2. But emp1 and emp2 are reference types. So if we change employees[0].name = "Sam Smith"   employees2[0] is also changed as they refer to the same object.

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3. What is the exact difference in the view model in MVVM and controller in MVC? Which pattern is preferable keeping in mind the code unit test coverage?

4. Please look at the code segment below. If we compile it what happens? Explain

2. Consider the following code snippet

3. What is the use of the dump function? Explain with example.

4. Please look at the code below. If we run method ., what will be the output and why?

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