How to prevent a 'Array index out of range' error?

Question

Is there a way, similar to using if let and/or optionals, to test whether you are about to index an empty buffer in Swift?

I don't know what it means. That is an error I get when I try to access an array index that doesn't exist yet; too high. The array might have 10 elements, but the app tries to access the 11th. — webmagnets
– webmagnets, Commented Mar 17, 2015 at 3:39
So it's an array, check the bounds of an array using the count property (array.count) GoZoner gives an example in his answer. — David Berry
– David Berry, Commented Mar 17, 2015 at 5:08

GoZoner · Accepted Answer · 2016-03-06 23:30:28Z

15

Define your own:

extension Array {
  func ref (i:Int) -> T? {
    return 0 <= i && i < count ? self[i] : nil
  }
}

The ref() function returns an optional, so it can be nil, and you can use the if let syntax to access the returned value from ref() when it exists. You would use this as such:

var myA = [10,20,30]
if let val = myA.ref(index) {
  // Use 'val' if index is < 3
}
else {
  // Do this if the index is too high
}

edited Mar 6, 2016 at 23:30

answered Mar 17, 2015 at 4:08

GoZoner

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2 Comments

webmagnets Over a year ago

I don't understand this very well. Can you show me how to use it and maybe what it is doing?

osrl Over a year ago

I think ref needs a better name. But I couldn't think one.

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