Beginning Swift Programming

10 Closures

WHAT YOU WILL LEARN IN THIS CHAPTER:                  

• What closures are
• Functions as special types of closures
• How to create a closure as a variable
• How to write a closure inline
• How to simplify closures using type inference
• How to simplify closures using shorthand argument names
• How to simplify closures using operator functions
• How to write a trailing closure
• How to use the Array’s three closure functions: map(), filter(), and reduce()
• How to declare and use closures in your functions

One of the important features in Swift is the closure. Closures are self-contained blocks of code that can be passed to functions to be executed as independent code units. Think of a closure as a function without a name. In fact, functions are actually special cases of closures.

Swift offers various ways to optimize closures so that they are brief and succinct. The various optimizations include the following:

• Inferring parameter types and return type
• Implicit returns from single-statement closures
• Shorthand argument names
• Trailing closure syntax
• Operator closure

NOTE  Closure is Swift’s answer to Objective-C’s block syntax and C#’s Lambda expressions.

UNDERSTANDING CLOSURES

The best way to understand closures is to use an example. Suppose you have the following array of integers:

	let numbers = [5,2,8,7,9,4,3,1]

Assume you want to sort this array in ascending order. You could write your own function to perform the sorting, or you could use the sorted() function available ...