Closure tuple does not support destructuring in Xcode 9 Swift 4

Question

After the gloss project for Swift 4 in Xcode 9

I am getting following error which i have no idea

Closure tuple parameter \'(key: _, value: _)

Answer 1

I just encountered this error as a result of using enumerated().map():

Closure tuple parameter does not support destructuring

I typed the code:

["foo"].enumerated().map

And then pressed Enter 3 times until Xcode autocompleted the closure boilerplate.

The autocomplete seemingly has a bug that causes the above error. The autocomplete produces double-parenthesis ((offset: Int, element: String)) rather than single-parenthesis (offset: Int, element: String).

I fixed it manually and was able to continue:

// Xcode autocomplete suggests:
let fail = ["foo"].enumerated().map { ((offset: Int, element: String)) -> String in
    return "ERROR: Closure tuple parameter does not support destructuring"
}

// Works if you manually replace the "(( _ ))" with "( _ )"
let pass = ["foo"].enumerated().map { (offset: Int, element: String) -> String in
    return "works"
}

Possibly the result of using Xcode 10.0 beta (10L176w)