Closures provide a powerful, flexible way for iOS developers to define and use functions in Swift, replacing the blocks used in its predecessor Objective-C. They provide self-contained modules of functionality that you can move around in your code, similar to the lambdas found in other programming languages. Crucially, closures can capture and store references to any constants and variables from the context in which they’re defined.

We use them to manage users’ log-in sessions, impose time-outs, display dates when content was posted and show the most recent publications to users. This is crucial to a variety of apps, from digital diaries to diet and exercise planners, and onto travel-booking resources. As our user bases become more geographically diverse, so time management gets even more important.