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 was 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

Q13. What is the type of value1 in this code?

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

• String
• Int
• null
• test.count

Q14. 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

Q15. 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.

Q16. 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.

Q17. 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

Q18. 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.

Q19. didSet and willSet are examples of \***\*\_\*\***?

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

Q20. 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.

Q21. 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.

Q22. 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.

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

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

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 was to ass 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 an optional type
• an instance of a function type
• all of these answers

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 test in this code?

var test = 1 == 1

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

Q33. What is the value of y?

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

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

Q34. What is the value of y?

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

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

Q35. 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.
• 0
• 1
• Larry

Q36. What is the value of test after this code executes?

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

• ABC
• 0
• 5
• name

Q37. What is the base class in this code?

class LSN : MMM {
}

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

Q38. 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 to 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

Q39. 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

Q40. 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

Q41. What is the inferred type of x?

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

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

Q42. 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.

Q43. How would you call a function that throws errors and also returns a value?

• !try
• try?
• try!
• ?try

Q44. 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.

Q45. 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

Q46. What is the value of t after this code is executed?

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

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

Q47. How do you designate a failable initializer?

• init?
• deinit
• init
• You can't.

Q48. What is printed when this code is executed?

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

• five
• 5a
• .asString()
• 5