swift.md

Swift Reference

typealias

typealias VoidVoidFunction = () -> ()

func doThis(_ f: VoidVoidFunction) {
    f()
}

Anonymous Functions

{
    () -> () in
    // Function body code below...
    print("Hello World!")
}

{
    (x: Int, y: Int) -> Int in
    return x + y
}

Inline anonymous function

func invokeFunc(x: Int, y: Int, _ f:(Int, Int) -> Int) {
    print(f(x, y))
}

invokeFunc(x: 10, y: 20, {
    (_ x: Int, _ y: Int) -> Int in
    return x + y
})

Omission of the return type

If the anonymous function's return type is already known to the compiler, you can omit the arrow operator and the specification of the return type

func invokeFunc(x: Int, y: Int, _ f:(Int, Int) -> Int) {
    print(f(x, y))
}

invokeFunc(x: 10, y: 20, {
    (_ x: Int, _ y: Int) in
    return x + y
})

Omission of the in expression when there are no parameters

If the anonymous function takes no parameters, and if the return type can be omitted, the in expression itself can be omitted

func invokeFunc(_ f:() -> ()) {
    f()
}

invokeFunc({
    print("Anonymous says hello")
})

Omission of the parameter types

If the anonymous function takes parameters and their types are already known to the compiler, the types can be omitted

func invokeFunc(x: Int, y: Int, _ f:(Int, Int) -> Int) {
    print(f(x, y))
}

invokeFunc(x: 10, y: 20, {
    (x, y) in
    return x + y
})

Omission of the parentheses

If the parameter types are omitted, the parentheses around the parameter list can be omitted

func invokeFunc(x: Int, y: Int, _ f:(Int, Int) -> Int) {
    print(f(x, y))
}

invokeFunc(x: 10, y: 20, {
    x, y in
    return x + y
})

Omission of the in expression when there are parameters

If the return type can be omitted, and if the parameter types are already known to the compiler, you can omit the in expression and refer to the parameters directly within the body of the anonymous function by using the magic names $0, $1, and so on, in order

func invokeFunc(x: Int, y: Int, _ f:(Int, Int) -> Int) {
    print(f(x, y))
}

invokeFunc(x: 10, y: 20, {
    return $0 + $1
})