LinkedIn Swift Assessment Answers

Swift

Q1. What is this code an example of?

let val = (Double)6

•  an error
•  typecasting
•  assignment
•  initialization

Q2. What is the error in this code?

let x = 5
guard x == 5 { return }

•  The guard is missing the else.
•  Nothing is wrong.
•  The guard is missing a then.
•  The comparison is wrong.

Q3. What is the raw/underlying type of this enum?

enum Direction {
  case north, south, east, west
}

•  There is none.
•  String
•  Any
•  Int

Q4. Why is dispatchGroup used in certain situations?

•  It allows multiple synchronous or asynchronous operations to run on different queues.
•  It allows track and control execution of multiple operations together.
•  It allows operations to wait for each other as desired.
•  all of these answers.

Q5. What is this code an example of?

let val = 5
print("value is: \(val)")

•  string interpolation
•  string compilation
•  method chaining
•  string concatenation

Q6. What are the contents of vals after this code is executed?

var vals = [10, 2]
vals.sort { (s1, s2) -> Bool in
  s1 > s2
}

•  [10, 2]
•  [2, 10]
•  nil
•  This code contains an error

Q7. What does this code print?

typealias Thing = [String, Any]
var stuff: Thing
print(type(of: stuff))

•  Dictionary<String, Any> (To print this than code in question has to be typealias Thing = [String: Any])
•  Dictionary
•  ERROR (If code in question is really like that.)
•  Thing

Q8. What is the value of y?

let x = ["1", "2"].dropFirst()
let y = x[0]

•  This code contains an error
•  1
•  2
•  nil

Q9. What is the value of test in this code?

var test = 1 == 1

•  TRUE
•  YES
•  1
•  This code contains an error

Q10. What is the value of y?

var x: Int?
let y = x ?? 5

•  5
•  0
•  nil
•  This code contains an error

Q11. What is the type of this function?

func add(a: Int, b: Int) -> Int { return a+b }

•  Int
•  (Int, Int) -> Int
•  Int
•  Functions don't have types.

Q12. What is the correct way to call this function?

func myFunc(_ a: Int, b: Int) -> Int {
  return a + b
}

•  myFunc(5, b: 6)
•  myFunc(5, 6)
•  myFunc(a: 5, b: 6)
•  myFunc(a, b)

Q13. The Codable protocol is _?

•  a combination of Encodable and Decodable
•  not a true protocol <<<<---Possibly correct as it's a typealias of Encodable and Decodable
•  required of all classes
•  automatically included in all classes

Q14. What is the type of value1 in this code?

let value1 = "\("test".count)"

•  String
•  Int
•  null
•  test.count

Q15. When a function takes a closure as a parameter, when do you want to mark is as escaping?

•  when it's executed after the function returns
•  when it's scope is undefined
•  when is's lazy loaded
•  all of these answers

Q16. What's wrong with this code?

class Person {
  var name: String
  var address: String
}

•  Person has no initializers.
•  Person has no base class.
•  var name is not formatted corrrectly.
•  address is a keyword.

Q17. What is the value of names after this code is executed?

let names = ["Bear", "Joe", "Clark"]
names.map { (s) -> String in
  return s.uppercased()
}

•  ["BEAR", "JOE", "CLARK"]
•  ["B", "J", "C"]
•  ["Bear", "Joe", "Clark"]
•  This code contains an error.

Q18. What describes this line of code?

let val = 5

•  a constant named val of type Int
•  a variable named val of type item
•  a constant named val of type Number
•  a variable named val of type Int

Q19. What is the error in this code?

extension String {
  var firstLetter: Character = "c" {
    didSet {
      print("new value")
    }
  }
}

•  Extensions can't add properties. // although extensions technically can't contain stored properties
•  Nothing is wrong with it.
•  didSet takes a parameter.
•  c is not a character.

Q20. didSet and willSet are examples of _?

•  property observers
•  key properties
•  all of these answers
•  newOld value calls

Q21. What is wrong with this code?

self.callback = {
  self.attempts += 1
  self.downloadFailed()
}

•  Use of self inside the closure causes retain cycle.
•  You cannot assign a value to closure in this manner.
•  You need to define the type of closure explicitly.
•  There is nothing wrong with this code.

Q22. How many values does vals have after this code is executed?

var vals = Set<String> = ["4", "5", "6"]
vals.insert("5")

•  three
•  four
•  eight
•  This code contains an error.

Q23. How can you avoid a strong reference cycle in a closure?

•  Use a capture list to set class instances of weak or unowned.
•  You can't, there will always be a danger of strong reference cycles inside a closure.
•  Initialize the closure as read-only.
•  Declare the closure variable as lazy.

Q24. What is wrong with this code?

if let s = String.init("some string") {
  print(s)
}

•  This String initializer does not return an optional.
•  String does not have an initializer that can take a String.
•  = is not a comparison.
•  Nothing is wrong with this code.

Q25. Which code snippet correctly creates a typealias closure?

•  typealias CustomClosure: () -> ()
•  typealias CustomClosure { () -> () }
•  typealias CustomClosure -> () -> ()
•  typealias CustomClosure -> () {}

Q26. How do you reference class members from within a class?

•  self
•  instance
•  class
•  this

Q27. All value types in Swift are _ under the hood?

•  structs
•  classes
•  optionals
•  generics

Q28. What is the correct way to add a value to this array?

var strings = [1, 2, 3]

•  all of these answers
•  strings.append(4)
•  strings.insert(5, at: 1)
•  strings += [5]

Q29. How many times will this loop be executed?

for i in 0...100 {
  print(i)
}

•  0
•  101
•  99
•  100

Q30. What can AnyObject represent?

•  an instance of any class
•  an instance of function type
•  all of these answers
•  an instance of an optional type

Q31. What does this code print?

typealias Thing = [String:Any]
var stuff : Thing
print(type(of:stuff))

•  Dictionary
•  ERROR
•  Thing
•  Dictionary<String, Any>

Q32. What is the value of t after this code is executed?

let names = ["Larry", "Sven", "Bear"]
let t = names.enumerated().first().offset

•  This code is invalid.
•  This code does not compile.
•  0
•  1
•  Larry

Q32. What is the value of test after this code executes?

let vt = (name: "ABC", val: 5)
let test = vt.0

•  ABC
•  0
•  5
•  name

Q33. What is the base class in this code?

class LSN : MMM {
}

•  MMM
•  LSN
•  There is no base class.
•  This code is invalid.

Q34. What does this code print to the console?

var userLocation: String = "Home" {
  willSet(newValue) {
  print("About to set userLocation to \(newValue)...")
  }

  didSet {
  if userLocation != oldValue {
  print("userLocation updated with new value!")
  } else {
  print("userLocation already set to that value...")
  }
  }
 }

 userLocation = "Work"

•  About to set userLocation to Work… userLocation updated with new value!
•  About to set userLocation to Work… userLocation already set to that value…
•  About to set userLocation to Home… userLocation updated to new value!
•  ERROR

Q35. What must a convenience initializer call?

•  a base class convenience initializer
•  either a designated or another convenience initializer
•  a designated initializer
•  none of these answers

Q36. Which object allows you access to specify that a block of code runs in a background thread?

•  DispatchQueue.visible
•  DispatchQueue.global
•  errorExample need to be labeled as throws.
•  DispatchQueue.background

Q37. What is the inferred type of x?

let x = ["a", "b", "c"]

•  String[]
•  Array<String>
•  Set<String>
•  Array<Character>

Q38. What is the value of oThings after this code is executed?

let nThings: [Any] = [1, "2", "three"]
let oThings = nThings.reduce("") { "\($0)\($1)" }

•  11212three
•  115
•  12three
•  Nothing, this code is invalid.

Q39. How would you call a function that throws errors and also returns a value?

•  !try
•  try?
•  try!
•  ?try

Q40. What is wrong with this code?

protocol TUI {
  func add(x1 : Int, x2 : Int) -> Int {
    return x1 + x2
  }
}

•  Protocol functions cannot have return types.
•  Protocol functions cannot have implementations.
•  Nothing is wrong with it.
•  add is a reserved keyword.

Q41. In this code, what are wheels and doors examples of?

class Car {
  var wheels: Int = 4
  let doors = 4
}

•  class members
•  This code is invalid.
•  class fields
•  class properties

Q42. How do you designated a failable initializer?

•  You cannot
•  deinit
•  init?
•  init

Q43. What is printed when this code is executed?

let dbl = Double.init("5a")
print(dbl ?? ".asString()")

•  five
•  5a
•  .asString()
•  5

Q44. In the function below, what are this and toThat examples of?

func add(this x: Int, toThat y: Int)->{}

•  none of these answers
•  local terms
•  argument labels
•  parameters names

Q45. What is wrong with this code?

for (key, value) in [1: "one", 2: "two"]{
  print(key, value)
}

•  The interaction source is invalid
•  The interaction variable is invalid
•  There is nothing wrong with this code
•  The comma in the print is misplaced

Q46. Which of these choices is associated with unit testing?

•  XCTest
•  all of these answers
•  @testable
•  XCAssert

Q47. In the code below, what is width an example of?

class Square{
  var height: Int = 0
  var width : Int {
    return height
  }
}

•  This code contains error
•  a closure
•  a computed property
•  lazy loading

Q48. What data type is this an example of?

let vals = ("val", 1)

•  a dictionary
•  a tuple
•  an optional
•  This code contains error

Q49. What is wrong with this code?

var x = 5
x = 10.0

•  You cannot assign a Double to a variable of type Int
•  x is undefined
•  x is a constant
•  x has no type

Q50. What will this code print to the console?

var items = ["a":1, "b":2, "c":"test"] as [String: Any]
items["c"] = nil
print(items["c"] as Any)

•  Any
•  test
•  1,2,3
•  nil

Q51. What is wrong with this code?

let val = 5.0 + 10

•  There is nothing wrong with this code
•  val is a constant and cannot be changed
•  5.0 and 10 are different types
•  There is no semicolon

Q52. How many parameters does the initializer for Test have?

struct Test{
  var score: Int
  var date: Date
}

•  zero
•  This code contains an error
•  two
•  Structs do not have initializers

Q53. What prints to the console when executing this code?

let x = try? String.init("test")
print(x)

•  nil
•  Nothing - this code contains an error
•  Optional("test")
•  test

Q54. How can you sort this array?

var vals = [1,2,3]

•  vals.sort { $0 < $1 }
•  vals.sort { (s1, s2) in s1 < s2 }
•  vals.sort(by: <)
•  all of these answers

Q55. DispatchQueue.main.async takes a block that will be

•  not executed
•  executed in the main queue
•  none of these answers
•  executed on the background thread

Q56. When is deinit called?

•  When a class instance needs memory
•  All of these answers
•  When the executable code is finished
•  When a class instance is being removed from memory

Q57. How do you declare an optional String?

•  String?
•  Optional[String]
•  [String]?
•  ?String

Q58. How many times this code will be executed? —OR— How many times will this loop be performed?

for i in ["0", "1"]{
  print(i)
}

•  one
•  two
•  three
•  This code does not compile

Q59. What does this code print?

let names = ["Bear", "Tony", "Svante"]
print(names[1]+"Bear")

•  1Bear
•  BearBear
•  TonyBear
•  Nothing, this code is invalid

Q60. What is true of this code?

let name: String?

•  name can hold only a string value.
•  name can hold either a string or nil value.
•  Optional values cannot be let constants.
•  Only non-empty string variables can be stored in name.

Q61. What is the value of val after this code is executed?

let i = 5
let val = i * 6.0

•  This code is invalid.
•  6
•  30
•  0

Q62. What does this code print?

enum Positions : Int {
  case first, second, third, other
}
print (Positions.other.rawValue)

•  3
•  0
•  other
•  nil

Q63. What is printed to the console when this code is executed?

"t".forEach { (char) in
    print(char)
}

•  nil
•  Nothing, since the code contains an error
•  t
•  zero

Q64. What prints when this code is executed?

let s1 = ["1", "2", "3"]
    .filter { $0 > "0" }
    .sorted { $0 > $1 }
print(s1)

•  []
•  ["3", "2", "1"]
•  [321]
•  ["1", "2", "3"]

Q65. What enumeration feature allows them to store case-specific data?

(Question does not make that much sense though. )

•  associated values
•  integral values
•  raw values
•  custom values

Q66. In the code below, AOM must be a(n) _?

class AmP : MMM, AOM {
  }

•  class
•  protocol
•  enumeration
•  struct