"Collection corresponding..." error on Swift 3 upgrade

Question

Here's a pre-Xcode-8 Swift call ..

func gappizeAtDoubleNewlines()
    {
    let t = self.text!
    var index = t.startIndex
    var follow = index.advancedBy(1)

    for i in 0 ..< (t.characters.count-4)
        {
        let r = index ... follow
        if ( t.substringWithRange(r) == "\n\n" )
            { alterLineGapHere(i) }

        index = index.advancedBy(1)
        follow = index.advancedBy(1)
        }
    }

using the automatic upgrade to Swift3, I got these errors...

in text,

func gappizeAtDoubleNewlines()
    {
    let t = self.text!
    var index = t.startIndex
    var follow = <#T##Collection corresponding to `index`##Collection#>.index(index, offsetBy: 1)

    for i in 0 ..< (t.characters.count-4)
        {
        let r = index ... follow
        if ( t.substring(with: r) == "\n\n" )
            { alterLineGapHere(i) }

        index = <#T##Collection corresponding to `index`##Collection#>.index(index, offsetBy: 1)
        follow = <#T##Collection corresponding to `index`##Collection#>.index(index, offsetBy: 1)
        }
    }

What is the solution in Swift3 ??

Sure thing – I have a habit of accidently answering questions in the comments :) — Hamish, Oct 03 '16 at 15:38

score 3 · Accepted Answer · answered Oct 03 '16 at 15:38

See SE-0065: 'Collections move their indices' – in this case you can just replace the editor placeholders with t:

func gappizeAtDoubleNewlines() {

    let t = self.text!
    var index = t.startIndex

    // Note that because substring(by:) takes a Range<String.Index>, rather than
    // a ClosedRange, we have to offset the upper bound by one more.
    var follow = t.index(index, offsetBy: 2)

    for i in 0 ..< (t.characters.count-4) {
        let r = index ..< follow
        if (t.substring(with: r) == "\n\n") {
            alterLineGapHere(i)
        }

        index = t.index(index, offsetBy: 1)
        follow = t.index(follow, offsetBy: 1)
    }
}

Although note that String isn't a Collection itself, it just implements some convenience methods for indexing that forward to t.characters, which is a Collection.

and for anyone googling, with the very latest Swift, I found this extension handy ... http://stackoverflow.com/a/39677704/294884 — Fattie, Oct 03 '16 at 15:44

"Collection corresponding..." error on Swift 3 upgrade

1 Answers1