Comment by bzbarsky | Hacker News Reader

Comment by bzbarsky | Hacker News Reader

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If s.index() returned nil, the "if" would test false and the s[i] would not be reached.

The problem is that it returns non-nil, but the _limit_ is broken in this case: using s.endIndex as a limit means you can get non-nil but bogus indices returned. And yes, this is the fault of the docs for using a broken last arg to the API, but there's no really clean way to use this API as designed, afaict. At least not if you want to limit to "end of string" as opposed to "some index into the string that I already know to be valid".

The index is not bogus, the API is working as designed. The example provided shows the use of the index, which I understand can be confusing because the index returned may not always be valid for this, but the index is decidedly valid. FWIW, since String is a BiderectionalCollection, this code works for what you are probably trying to do:

  let s = "Swift"
  if !s.isEmpty,
      let index = s.index(s.startIndex, offsetBy: 5, limitedBy: s.index(before: s.endIndex)) {
    print(s[index])
  }

I am sure the equivalent code in other languages, barring Python, is going to be similarly verbose.

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