Today, most major programming languages have functionalities similar to what closures offer. Some of these implementations are really hard to use (Objective-C blocks), while others are easy (Java lambdas and C# delegates). I found that the functionality that closures provide is especially useful when developing frameworks. I have also used them extensively when communicating with remote services over a network connection. While blocks in Objective-C are incredibly useful (and I have used them quite a bit), their syntax used to declare a block was absolutely horrible. Luckily, when Apple was developing the Swift language, they made the syntax of closures much easier to use and understand.
In this chapter, we will cover the following topics:
An introduction to closures
Defining a closure
Using a closure
Several useful examples of closures
How to avoid strong reference cycles with closures