Swift: Function vs Closure

Swift: Function vs Closure

In Swift, both functions and closures are self-contained blocks of code that can be passed around and used in your programs. While functions have a defined name and structure, closures are anonymous and can capture values from their surrounding context, making them more flexible for inline use.

Code

// A simple named function that adds two numbers
func add(a: Int, b: Int) -> Int {
  return a + b
}

// Using the function
let sum = add(a: 3, b: 5)

// A closure that does the same addition, assigned to a variable
let addClosure: (Int, Int) -> Int = { (a, b) in
  return a + b
}

// Using the closure
let closureSum = addClosure(3, 5)

// Closures can capture values from their context
func makeIncrementer(amount: Int) -> () -> Int {
  var total = 0
  // This closure captures 'total' and 'amount'
  return {
    total += amount
    return total
  }
}

let incrementByTen = makeIncrementer(amount: 10)
incrementByTen()  // returns 10
incrementByTen()  // returns 20

Key Points

• Functions are named blocks of code, while closures are anonymous and can be assigned to variables.
• Closures can capture and store references to variables from their surrounding context.
• Closures provide flexibility for inline, concise code, especially for callbacks and functional programming patterns.
• Both functions and closures share the same type syntax and can be used interchangeably in many situations.