> On Apr 13, 2017, at 3:56 AM, Andrew Hart via swift-evolution
> <[email protected]> wrote:
>
> Recently I’ve been considering the lack of safety around array indexes. Swift
> is designed with safety in mind, so this example would not compile:
>
> var myString: String? = “hello”
> myString.append(“ world!”)
>
> The string is optional, not guaranteed to exist, so the last line requires a
> “!” to force-unwrap it.
>
>
>
> public func tableView(_ tableView: UITableView, numberOfRowsInSection
> section: Int) -> Int {
> let section = self.sections[section]
>
> return section.items.count
> }
>
> In this example, we could provide a section number that goes beyond the
> bounds of the self.sections array, without any warning.
>
> My suggestion is perhaps arrays should by default return an optional when
> given an index, and of course they’d support forced-unwrapping too. So you
> could then do this:
>
> let section = self.sections[section]
> if section == nil {
> return 0
> } else {
> return section!.items.count
> }
>
> Or you could do this:
>
> let section = self.sections[section]!
>
> return section.items.count
>
> Of course this would be less convenient in a lot of cases, but this is the 1
> place where apps seem to encounter a crash, crashing for the same reason
> that’s especially avoided across most of the rest of Swift.
My understanding is that we need the current behavior to meet performance
goals. We’ve discussed adding a “safe” subscript before, but the discussion
usually fizzles out when no clear winner for the argument label emerges.
- Dave Sweeris
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