CODEWITHSUNDEEP
swiftswift3
PrepareFor
PrepareFor

Reputation: 2598

Swift - What Type is '()'?

I tested some code to understand completion handlers, and I found that there are types such as ()->() and ().

I know ()->() means "no parameters and no return value"; but what type is ()?

If I define a function like this: 

func sayHello(){
  print("hello")
}

and then check the type:

type(of: sayHello) // ()->()
type(of: sayHello()) // ()

Is "function execution" (()), a type?

Upvotes: 1

Views: 67

Answers (2)

user3441734
user3441734

Reputation: 17572

typealias Void = ()

The return type of functions that don't explicitly specify a return type; an empty tuple (i.e., ()).

When declaring a function or method, you don't need to specify a return type if no value will be returned. However, the type of a function, method, or closure always includes a return type, which is Void if otherwise unspecified.

Use Void or an empty tuple as the return type when declaring a closure, function, or method that doesn't return a value.

Upvotes: 0

rmaddy
rmaddy

Reputation: 318924

What you are really asking is why does type(of: sayHello()) result in ().

Start by thinking about what sayHello() does. It actually calls the function. So type(of:) is telling you the type of the result of that call. Since the return type of sayHello is Void, the type is (). It's basically the second () of () -> () seen in the first call to type(of:).

If you change sayHello to have a return type of Int instead of Void, then the 2nd type(of:) returns Int instead of (). And the 1st type(of:) would change from () -> () to () -> Int.

tl;dr - () represents Void. The return type of calling sayHello().

Upvotes: 3

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