Exploring closures

A closure, like a function, contains a sequence of instructions and can take arguments and return values. However, closures don't have names. The sequence of instructions in a closure is surrounded by curly braces ({ }), and the in keyword separates the arguments and return type from the closure body.

Closures can be assigned to a constant or variable, so they're handy if you need to pass them around inside your program. For instance, let's say you have an app that downloads a file from the internet, and you need to do something to the file once it has finished downloading. You can put a list of instructions to process the file inside a closure and have your program execute it once the file finishes downloading.

To learn more about closures, visit https://docs.swift.org/swift-book/documentation/the-swift-programming-language/closures/.

You'll now write a closure that applies a calculation on each...