Control Flow: if, when, for, while

If Expression

                  // Traditional usage 
var max = a 
if (a < b) max = b
​
// With else 
var max: Int
if (a > b) {
    max = a
} else {
    max = b
}
 
// As expression 
val max = if (a > b) a else b
                

                    // Traditional usage 
var max = a 
if a < b { max = b }
​
// With else 
var max: Int
if a > b {
    max = a
} else {
    max = b
}
 
let max = a > b ? a : b

                  

                  val max = if (a > b) {
    print("Choose a")
    a
} else {
    print("Choose b")
    b
}
                

                    let max: Int
if a > b {
    print("Choose a")
    max = a
} else {
    print("Choose b")
    max = b
}

                  

When Expression

                  when (x) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> { // Note the block
        print("x is neither 1 nor 2")
    }
}
                

                    switch x {
case 1:
    print("x == 1")
case 2:
    print("x == 2")
default:
    print("x is neither 1 nor 2")
}

                  

                  when (x) {
    0, 1 -> print("x == 0 or x == 1")
    else -> print("otherwise")
}
                

                    switch x {
case 0, 1:
    print("x == 0 or x == 1")
default:
    print("otherwise")
}

                  

                  when (x) {
    parseInt(s) -> print("s encodes x")
    else -> print("s does not encode x")
}
                

                    switch x {
case is Int:
    print("s encodes x")
default:
    print("s does not encode x")
}

                  

                  when (x) {
    in 1..10 -> print("x is in the range")
    in validNumbers -> print("x is valid")
    !in 10..20 -> print("x is outside the range")
    else -> print("none of the above")
}
                

                    switch x {
case 1...10:
    print("x is in the range")
case let x where validNumbers.contains(x):
    print("x is valid")
case let x where 10...20 ~= x:
    print("x is outside the range")
default:
    print("none of the above")
}

                  

                  fun hasPrefix(x: Any) = when(x) {
    is String -> x.startsWith("prefix")
    else -> false
}
                

                    func hasPrefix(x: Any) -> Bool {
    switch x {
    case let x as String:
        return x.starts(with: "prefix")
    default:
        return false
    }
}

                  

                  when {
    x.isOdd() -> print("x is odd")
    y.isEven() -> print("y is even")
    else -> print("x+y is odd.")
}
                

                    if x.isOdd() {
    print("x is odd")
}else if y.isEven() {
    print("y is even")
}else {
    print("x+y is odd.")
}

                  

                  fun Request.getBody() =
        when (val response = executeRequest()) {
            is Success -> response.body
            is HttpError -> throw HttpException(response.status)
        }
                

                    extension Request {
    
    func getBody() throws -> Body {
        let response = executeRequest()
        
        switch response {
        case .success(let body):
            return body
        case .error(let status):
            throw .httpException(status)
        }
    }
}
        

                  

For Loops

                  for (item in collection) print(item)
                

                    for item in collection {
    print(item)
}

                  

                  for (item: Int in ints) {
    // ...
}
                

                    for item in ints {
    // ...
}

                  

                  for (i in 1..3) {
    println(i)
}
for (i in 6 downTo 0 step 2) {
    println(i)
}
                

                    for i in 1...3 {
    print(i)
}
for i in stride(from: 6, through: 0, by: -2) {
    print(i)
}

                  

                  for (i in array.indices) {
    println(array[i])
}
                

                    for i in array.indices {
    print(array[i])
}

                  

                  for ((index, value) in array.withIndex()) {
    println("the element at $index is $value")
}
                

                    for (index, value) in array.enumerated() {
    print("the element at \(index) is \(value)")
}

                  

While Loops

                  while (x > 0) {
    x--
}
​
do {
    val y = retrieveData()
} while (y != null) // y is visible here!
                

                    while x > 0 {
    x -= 1
}
​
var y: String?
repeat {
    y = retrieveData()
} while y != nil