On May 4, 2017, at 8:51 AM, André Videla via swift-evolution
<swift-evolution@swift.org> wrote:
>
> You can do this trivially with drop. But enumerated from has one nice
> property:
>
> myArray.enumerated().dropFirst(6) // counts from 6
>
> myArray.dropFirst(6).enumerated() // counts from 0
>
> Those two lines do very different things even though they look similar
Neither of those does what the proposed enumerated(from:) does, if I understand
correctly:
let a = [1, 2, 3, 4, 5]
let result = a.enumerated().dropFirst(2)
/*
(offset: 2, element: 3)
(offset: 3, element: 4)
(offset: 4, element: 5)
*/
let result2 = a.dropFirst(2).enumerated()
/*
(offset: 0, element: 3)
(offset: 1, element: 4)
(offset: 2, element: 5)
*/
let proposed = a.enumerated(from: 2)
/*
(offset: 2, element: 1)
(offset: 3, element: 2)
(offset: 4, element: 3)
(offset: 5, element: 4)
(offset: 6, element: 5)
*/
The enumerated(from:) name is not clear; it reads (to me) like it’s going to
enumerate elements starting at the Nth element. What it actually does (as
proposed) is start counting at N, instead of counting at 0.
I’m not convinced this is a valuable addition to the language. The use cases
are not widely applicable, and if you need it it’s easy to get the same results
in a way that avoids the confusion.
let a = [1, 2, 3, 4, 5]
let result = a.enumerated().map { (idx, element) in
return (idx+2, element)
}
// OR
for (idx, element) in a.enumerated() {
let offsetIndex = idx + 2
// Use offsetIndex how you will
}
-BJ_______________________________________________
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