Appending '[element]' recursively

Using Swift
1

Hi everyone!

I’m migrating some code from Swift 2.2. to Swift 3 and something weird happened.

Is this is a bug or I’m missing something?

// Swift 2.2

func quickSort(_ array: [Int]) -> [Int] {
    guard array.count > 1 else {
        return array
    }

    let (pivot, rest) = (array.first!, array.dropFirst())

    let lessThan = rest.filter({ $0 < pivot })
    let greaterThanOrEqual = rest.filter({ $0 >= pivot })

    // Can use ‘[pivot]' here, no problem at all
    return quickSort(lessThan) + [pivot] + quickSort(greaterThanOrEqual)
}

// Swift 3

func quickSort(_ array: [Int]) -> [Int] {
    guard array.count > 1 else {
        return array
    }

    let (pivot, rest) = (array.first!, array.dropFirst())

    let lessThan = rest.filter({ $0 < pivot })
    let greaterThanOrEqual = rest.filter({ $0 >= pivot })

    // Cannot use ‘[Int]' here, as in Swift 2.2
    // Error says 'Int' is not convertible to '[Int]'
    let pivotArray = [pivot]
    return quickSort(lessThan) + pivotArray + quickSort(greaterThanOrEqual)
}

Best,

— A

2

Hi Adriano,

This code compiles with the current git master. Could you
double-check and post the exact error you are getting?

Dmitri

···

On Mon, Jun 27, 2016 at 7:48 AM, Adriano Ferreira via swift-users <swift-users@swift.org> wrote:

// Swift 3

func quickSort(_ array: [Int]) -> [Int] {
    guard array.count > 1 else {
        return array
    }

    let (pivot, rest) = (array.first!, array.dropFirst())

    let lessThan = rest.filter({ $0 < pivot })
    let greaterThanOrEqual = rest.filter({ $0 >= pivot })

    // Cannot use ‘[Int]' here, as in Swift 2.2
    // Error says 'Int' is not convertible to '[Int]'
    let pivotArray = [pivot]
    return quickSort(lessThan) + pivotArray + quickSort(greaterThanOrEqual)
}

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/

3

Hi,

So, I tried :

// Swift 3

func quickSort(_ array: [Int]) -> [Int] {
    guard array.count > 1 else {
        return array
    }

    let (pivot, rest) = (array.first!, array.dropFirst())

    let lessThan = rest.filter({ $0 < pivot })
    let greaterThanOrEqual = rest.filter({ $0 >= pivot })

    // If a separate the sorting into variables rather than
    // calling them direct before 'return' it works
    let lessThanSorted = quickSort(lessThan)
    let greaterThanOrEqualSorted = quickSort(greaterThanOrEqual)

    return lessThanSorted + [pivot] + greaterThanOrEqualSorted
}

Here the exact error I’m getting:

Thanks for helping.

— A

1422×460 54.6 KB

···

On Jun 27, 2016, at 12:38 PM, Dmitri Gribenko <gribozavr@gmail.com> wrote:

On Mon, Jun 27, 2016 at 7:48 AM, Adriano Ferreira via swift-users > <swift-users@swift.org> wrote:

// Swift 3

func quickSort(_ array: [Int]) -> [Int] {
   guard array.count > 1 else {
       return array
   }

   let (pivot, rest) = (array.first!, array.dropFirst())

   let lessThan = rest.filter({ $0 < pivot })
   let greaterThanOrEqual = rest.filter({ $0 >= pivot })

   // Cannot use ‘[Int]' here, as in Swift 2.2
   // Error says 'Int' is not convertible to '[Int]'
   let pivotArray = [pivot]
   return quickSort(lessThan) + pivotArray + quickSort(greaterThanOrEqual)
}

Hi Adriano,

This code compiles with the current git master. Could you
double-check and post the exact error you are getting?

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/

4

I see. I think this is a compiler bug, I filed
[SR-1914] Array '+' fails to type check · Issue #44523 · apple/swift · GitHub . Thanks!

Dmitri

···

On Mon, Jun 27, 2016 at 9:44 AM, Adriano Ferreira <adriano.ferreira@me.com> wrote:

Here the exact error I’m getting:

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/

5

Thanks Dmitri.

If use typecasting it seems to work again. Take a look below:

// Swift 3

func quickSort(_ array: [Int]) -> [Int] {
    guard array.count > 1 else {
        return array
    }

    let (pivot, rest) = (array.first!, array.dropFirst())

    let lessThan = rest.filter({ $0 < pivot })
    let greaterThanOrEqual = rest.filter({ $0 >= pivot })

    // If I typecast ‘[pivot]’ to ‘[Int]' it now works
    return quickSort(lessThan) + ([pivot] as [Int]) + quickSort(greaterThanOrEqual)
}

Cheers,

— A

···

On Jun 27, 2016, at 1:01 PM, Dmitri Gribenko <gribozavr@gmail.com> wrote:

On Mon, Jun 27, 2016 at 9:44 AM, Adriano Ferreira > <adriano.ferreira@me.com> wrote:

Here the exact error I’m getting:

I see. I think this is a compiler bug, I filed
https://bugs.swift.org/browse/SR-1914 . Thanks!

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/