swift-quiz.md

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"]