Functions and closures are first-class objects in Swift: you can store them, pass them as arguments to functions, and treat them as you would any other value or object. Passing in closures as completion handlers is a common pattern in many APIs we all know and love.
When you pass a closure into a function in Swift 3, there’s a new wrinkle: the compiler assumes closure parameters are non-escaping by default. What does this mean? What’s the difference between an escaping and a non-escaping closure?