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Start your free trialOmar De Yamlor
10,980 Pointstype annotation: ([Int]) ?
Hi, I am having trouble understanding the type of $0:
let numbers = [[1,2,3], [4,5,6], [7,8,9]]
let numbersFlatMap = numbers.flatMap { return $0 }
where $0 is declared as a constant: let $0: ([Int])
2 Answers
Caleb Kleveter
Treehouse Moderator 37,862 PointsThe parentheses are added around any type that is passed into a closure. They make no difference to the code and can be ignored.
If you look at the numbers
value, you will see it has a type [[Int]]
, or an array of an array of ints. .flatMap
takes each element of the parent array and passes it into a closure. This is type [Int]
, or an array of ints.
Hope this answers your question.
Omar De Yamlor
10,980 PointsHi Jhoan, thanks for your reply ! I was trying to understand the closure shorthand syntax by writing it in plain syntax.
let numbersFlatMap = numbers.flatMap({ (value: ([Int])) in
return value
})
I have no idea why the type of value is written as an array inside a pair of parenthesis :/
Jhoan Arango
14,575 PointsJhoan Arango
14,575 PointsOmar,
Would you please give me more context on the question ?