Functions and Closures in Swift

Here are top 13 things to know about Functions in Swift.

Photo by Joan Gamell on Unsplash

In Swift, you define functions to perform tasks with data.

1. Functions let you organize your code into small, repeatable chunks, like so:

func sayHello() { 
  print("Hello")
}
sayHello() // prints "Hello"

2. Functions can return a value to the code that calls them, it returns by using the arrow (->) symbol:

func usefulNumber() -> Int { 
  return 123
}
let anUsefulNumber = usefulNumber() // 123

3. You can pass parameters to a function inside the parentheses, which it’s able to use to do work.

func addNumbers(firstValue: Int, secondValue: Int) -> Int { 
  return firstValue + secondValue
}
 let result = addNumbers(firstValue: 1, secondValue: 2) // 3

4. A function can return a single value, as we’ve already seen, but it can also return multiple values, in the form of a tuple. When you call a function that returns a tuple, you can access its value by index or by name (if it has them):

func processNumbers(firstValue: Int, secondValue: Int) -> (doubled: Int, quadrupled: Int)
{
  return (firstValue * 2, secondValue * 4) 
}
// Accessing by number:
processNumbers(firstValue: 2, secondValue: 4).1 // = 16
// Same thing but with names…