3.4 Switch Statements

Statement switch

• can use any data type: Int, String(case sensitive), Tuple…
  
• cases must be exhaustive (use default or list all options)
  
• cases can use range operators (ie. 0...3, 4...6)
  
• no implicit fallthrough → break is understood

// -> Error: 404
var statusCode = 404
var errorString = "Error: "

switch statusCode {
case 100:
  errorString += "Info, 100."
// compound case
case 201, 204:
  errorString += "No content 2xx."
// range case
case 400...417:													
  errorString += "\(statusCode)"
default:
  errorString = "\(statusCode) Unknown."
}

• statusCode passed into switch print via string interpolation
  
• if multiple cases are valid, only 1st evaluated is executed unless fallthrough is used

Tuple Matching switch

// -> That dog is 7
let dogInfo1 = (7, "Fido")

switch dogInfo1 {
// no, due to case sensitivity
case (7, "fido"):
  "fido is 7"
// "_" -> wildcard
case (7, _):
  "That dog is 7"
default:
  "Default dog"
}

Value Bindings switch var let

• assign a var/con within a case that is only valid at that point
  
• bound values are automatically evaluated as true/correct

// -> My dog Maxx is 8
let dogInfo2 = (7, "Max")

switch dogInfo2 {
// 1st tuple value bound to age
case (let age, "max"):          
  "That's Max who is \(age)"
// replaces default|assigns multiple
case var (age, name):            
  age += 1
  name = "Maxx"
  "My dog \(name) is \(age)"
}

• move var outside parenthesis to bind all values
  
• default isn’t necessary if all options are bound

Value Bindings and where clause

• allows use of a conditional on bound vars/cons

// -> Spot is 7
let dogInfo3 = (7, "Spot")

switch dogInfo3 {
case let (_, name) where name == "spot":
	"Is that spot?"
case let (age, name) where age == 7:
	"\(name) is \(age)"
default:
	"default dog"
}

• default still needed due to the where clause

if case and implied where clause

• focuses on a single condition, doesn’t use default

// -> Cool and...
let age = 25

if case 18...35 = age, age >= 21 {
	print("Cool and can drink")
}

// if case converted to a basic if
if (age >= 18) && (age <= 35) && (age >= 21) {
	print("Cool and can drink")
}