What does $0.1, $0.0, etc. mean in Swift?

Question

I saw a dictionary data, its value is like:

var myDict = ["name": "John",
              "age": 28]

I see a code like below:

myDict.flatMap {
           let a = $0.0
           let b = $0.1
           ...
 }

What does $0.0 mean? What does $0.1 mean? What is the difference between $0 and $0.1?

Answer 1

$0 is a shorthand name for first argument passed to closure. In this case, as you're mapping a Dictionary, that argument is a tuple - hence $0.0 is a key, and $0.1 is a value

For more info on shorthand argument names, see Swift documentation on closures