Swift: How to check a variable exists (esp. index of array)

Question

I'm trying to check whether a variable (or rather a particular index of an array) exists in Swift.

If I use

if let mydata = array[1] {

I get an error if the index has a value, and a crash if it doesn't.

If I use

if array[1] != nil {

I get compiler warnings and/or crashes.

Essentially, I'm just trying to get command line arguments (which are any filename) and check whether they have been included or not. All the examples for command line arguments I've seen use switch/case statements, but to check for known text, rather than varying filenames.

Im still getting Index out of range errors in Xcode with the following:

if arguments.count > 1 {
    var input = arguments[2]
} else {
}

You have to check if the array contains more than one item: if array.count > 1 { let mydata = array[1] ... — vadian
– vadian, Commented Sep 8, 2017 at 18:57

elisar4 · Accepted Answer · 2017-09-08 18:58:12Z

5

try this:

extension Collection where Indices.Iterator.Element == Index {

    subscript (safe index: Index) -> Generator.Element? {
        return indices.contains(index) ? self[index] : nil
    }
}

then:

if let value = array[safe: 1] {
    print(value)
}

now you can even do:

textField.text = stringArray[safe: anyIndex]

that would not cause a crash because textField.text can be nil, and [safe:] subscript always returns value if exists or nil if not exists

answered Sep 8, 2017 at 18:58

elisar4

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Comments

Musa almatri · Accepted Answer · 2017-09-08 22:22:17Z

2

if index < myData.count {
  // safe to access 
  let x = myData[index]
}

edited Sep 8, 2017 at 22:22

Musa almatri

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answered Sep 8, 2017 at 18:58

DoesData

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2 Comments

benwiggy Over a year ago

Yes, that's certainly the obvious (Doh!) method. I'm intrigued as to how you're supposed to do it outside of an array, just for a general variable, though. My whole time with Swift is setting up contingencies for whether things exist or not.

Musa almatri Over a year ago

I think you meant: index < myData.count

Musa almatri · Accepted Answer · 2017-09-08 19:16:08Z

1

Simply, To check for index :

if index < array.count {
// index is exist

let data = array[index]

}

edited Sep 8, 2017 at 19:16

answered Sep 8, 2017 at 19:11

Musa almatri

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2 Comments

benwiggy Over a year ago

In the context of filenames: I'm looking to see whether the argument has been included, or not. If included, I don't know what filename someone will use, so can't use contains. But useful to know about contains nonetheless.

Musa almatri Over a year ago

I have edited my answer, index should be less than the array.count unlike the selected answer where the index is greater than the array count!

Mo Abdul-Hameed · Accepted Answer · 2017-09-08 19:27:17Z

0

You can use contains method to check whether a value exists in an array or not.

For example:

let expenses = [21.37, 55.21, 9.32, 10.18, 388.77, 11.41]
let hasBigPurchase = expenses.contains { $0 > 100 } // hasBigPurchase is a boolean saying whether the array contains the value or not.

Check its documentation for more information.

edited Sep 8, 2017 at 19:27

answered Sep 8, 2017 at 18:57

Mo Abdul-Hameed

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1 Comment

Kevin Over a year ago

That doesn't seem to be related to what the OP is asking. He's asking how to tell whether an index is valid.

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