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=$0.0let b=$0.1...}

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

  • Show the code where a and b variables are used.– kiranderSep 28 '17 at 13:28

$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

  • 3
    For better readability you should use $0.key for the key and $0.value for the value.– Leo DabusSep 28 '17 at 13:34
  • 4
    Or flatMap { (key, value) in ... }– Martin RSep 28 '17 at 13:37
  • Also parentheses it is not needed key, value in– Leo DabusSep 28 '17 at 13:39
  • Why do you say argument is a tuple? Isn't tuple value comma separated e.g. (3,4)? Dictionary's mapping argument is colon separated e.g. ("name":"John"). Are you saying tuple could also be colon separated e.g. (3:4)?– Leem.finSep 28 '17 at 22:19

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