Swift: definition and syntax of functions vs. closures

Question

Is this a function or a closure?

let triple: Int -> Int = {
    (number: Int) in // What is this?
    let result = 3 * number
    number
    return result
}

triple(1)

Answer 1

Swift Closures are defined as follows:

{ (parameters) -> return type in
    statements
}

Thus, your code sample is considered a closure by definition. However, I would rewrite it as follows by moving the return type within the curly braces:

let triple = {
  (number: Int) -> Int in
  let result = 3 * number  
  number
  return result
}

triple(1)

The parameters and return type begin after the opening curly brace and end before the in keyword and the body of the closure begins after the in keyword and ends at the closing curly brace. Next, I would recommend downloading and reading iBook from iTunes which can be found at the following location:

https://itunes.apple.com/us/book/swift-programming-language/id881256329?mt=11