The document discusses several interesting features of the Swift programming language, including type inference, mutability, optionals, named parameters, enumerations, switch statements, closures, and generics. Type inference allows variable types to be inferred from values rather than explicitly declared. Optionals handle the absence of values and can be conditionally unwrapped. Closures provide block syntax similar to Objective-C but with additional optional syntax. Generics allow structures to work with different types rather than a single type.

1. A Few Interesting
Things In Swift
Ara Hacopian
B’more on Rails
6/10/2014

2. Ara Hacopian
http://www.smartlogic.io
http://www.twitter.com/ahacop
http://www.github.com/ahacop
SmartLogic

3. Some Cool Stuff
● Type Inference
● Explicit Mutability
● Optionals
● Named Parameters
● Enumerations
● Exhaustive Switch
● Closures
● Generics

4. Type Inference
You can do this:
var x : Int = 0
var y : String = “foobar”
var z : Bool = true
Or, you can just do this:
var x = 0
var y = “foobar”
var z = true

5. Type Inference
var x = 1
x = “quux” ← COMPILER ERROR

6. Typed Collections
var mammals: String[] = [“dog”, “cat”]
var people = [“dan”, “eric”, “tom”]
var numbers = [1, 2, 3]
numbers.append(“ara”) ←COMPILER ERROR

7. Explicit Mutability
var x = 0
x = 1
x // x == 1
let y = 0
y = 1 ← COMPILER ERROR

8. Never Be Nil
var x : Int = 0
x = nil ← COMPILER ERROR

9. Optionals
Optionals handle the absence of a value.
Either:
1. there is some value, and it equals x
var foo : Int? = 41 // { Some 41 }
1. or, there is no value at all
var bar : Int? // nil

10. Optional Declaration
var intOptional : Int?
var stringOptional : String?
var boolOptional : Bool?

11. Optionals: Unwrapping
You can unwrap the value contained in the
optional by using the bang operator, like so:
var foo : Int? = 41
foo! == 41 // true
But if it’s nil, you will get a runtime error,
so don’t do that.

12. Optional Binding
var possibleNumber = "2"
if let actualNumber =
possibleNumber.toInt() {
println("(possibleNumber) has an integer
value of (actualNumber)")
} else {
println("(possibleNumber) could not be
converted to an integer")
}

13. Optional Chaining
class Person {
var name : String
var address : Address?
init(name:String, atAddress address:Address?=nil) {
self.name = name
self.address = address
}
}
class Address {
func sendLetter() {
println("Sent a letter!")
}
}
let ara = Person(name: "Ara")
let paul = Person(name: "Paul", atAddress:Address())
let people = [ara, paul]
for person in people {
person.address?.sendLetter()
}

14. External Param Names
func join(
string s1: String,
toString s2: String,
withJoiner joiner: String) -> String {
return s1 + joiner + s2
}
join(string: "hello", toString: "world",
withJoiner: ", ")

15. Enumerations
enum Compass {
case North, South, West, East
}
enum Status {
case OnTime, Delayed(Int, String)
}

16. Exhaustive Switch
In Swift, the compiler enforces that a switch statement contains a case
for every possible value for that type.
enum Status {
case OnTime, Delayed(Int, String)
}
let trainStatus = Status.Delayed(5, “banana on tracks”)
switch trainStatus {
case .OnTime:
println(“Train is on time!”)
case .Delayed(let minutes, let reason):
println(“Train delay: (minutes) minute(s), Reason: (reason)”)

17. Closures
Just like blocks in ObjC...but there’s a lot of optional syntax.
let names = ["Paul", "Ara", "Eric", "Tom", "Dan"]
func backwards(s1: String, s2: String) -> Bool {
return s1 > s2
}
1. sort(names, backwards)
2. sort(names, { (s1: String, s2: String) -> Bool in return s1 > s2
})
3. sort(names, { s1, s2 in return s1 > s2 } )
4. sort(names, { s1, s2 in s1 > s2 } )
5. sort(names, { $0 > $1 } )
6. sort(names, >)

18. Generics
struct IntStack {
var items = Int[]()
mutating func push(item: Int) {
items.append(item)
}
mutating func pop() -> Int {
return items.removeLast()
}
}

19. Generics
struct Stack<T> {
var items = T[]()
mutating func push(item: T) {
items.append(item)
}
mutating func pop() -> T {
return items.removeLast()
}
}

20. Questions?
http://www.smartlogic.io/
http://www.twitter.com/ahacop
http://www.github.com/ahacop