This document discusses closures and callbacks in Swift. It shows how functions can be passed as parameters to other functions, including examples of passing simple functions that return strings and functions that modify external variables. It also demonstrates shorthand syntax for writing closures and using callbacks with success and failure handlers.

1. Closure

2. First Class Function
func toStr(x: Int) -> String {
return "(x)"
}
toStr(3)
// functions can be assigned to a variable.
let toStr2 = {
(x: Int) -> String in
return "(x)"
}
toStr2(4)
Syntax Sugar

3. Pass a function as a parameter
let toStr = {
(x: Int) -> String in
return "(x)"
}
let toStr2 = {
(x: Int) -> String in
return "a(x)"
}
toStr(5)
toStr2(5)
func ajax(callback: (x: Int) -> String) {
callback(x: 10)
}
ajax(toStr) // 10
ajax(toStr2) // a10
type of the function
((x:Int) -> String)

4. lambda calculas
ajax({(param: Int) -> String in
return “(param)”
})
ajax({(param: Int) -> String in
return “($0)”
})
ajax({(param: Int) -> String in
return “($0)”
})
ajax(){“($0)”}
Complete
Short Hand

5. Closure
var result = 0 // caller’s result
ajax({
result++
})
func ajax(callback: ()->()) {
var result = 10 // nothing to do with the caller’s result
callback()
callback()
}
println(result) // 2, not 12

6. Callback
var result: String
ajax(
{
result = $0
},
fail:{
result = “NG”
}
)
func ajax(ok: (x:String)->(), fail fail:()->()) {
if let ret = get_string_via_ajax()
{
ok(x:ret)
} else {
fail()
}
}

7. map (transformer)
let list = [1, 2, 3]
list.map({$0 x 3}) // [3, 6, 9]
list.map(){$0 x 3}
list.map{$0 x 3}