Swift 3 – find number of calendar days between two dates

In Swift 5 there is a simple one-liner to get the number of days (or any other DateComponent) between two dates:

let diffInDays = Calendar.current.dateComponents([.day], from: dateA, to: dateB).day

Note: As pointed out in the comments, this solution measures the 24h periods and therefore requires at least 24h between dateA and dateB.