How to generate a random 4 digit number in Swift? [duplicate]

This question already has an answer here:

• What is the easiest way to generate random integers within a range in Swift? 2 answers

guys! I can't understand how to make the function generate ONLY 4 digit numbers, without generating 2, 3, even 1 digit numbers. I do it in Swift. Please, help me to realize it. Will be happy to see source code as an example :)