How to change the element of array in swift

Question

I'm having difficulty with this function:

func sort(source: Array<Int>!) -> Array<Int>! {
   source[0] = 1
    ......
    return source
}

An error happens:

Why can't I directly assign the value to the specific element in the array?

If you want to modify the array that was passed in, add the inout keyword: func sort(inout source: [Int]) and call it like this sort(source: &myArray). — vacawama
– vacawama, Commented Jun 11, 2016 at 13:30
Be aware that the code crashes if source is nil or empty. — vadian
– vadian, Commented Jun 11, 2016 at 13:30

user887210user887210 · Accepted Answer · 2016-06-11 13:20:43Z

1

The variable sort is immutable because it's a parameter. You need to create a mutable instance. Also, there's no reason to have the parameter and return value as implicitly unwrapped optionals with the ! operator.

func sort(source: Array<Int>) -> Array<Int> {
   var anotherSource = source // mutable version
   anotherSource[0] = 1
   ......
   return anotherSource
}

answered Jun 11, 2016 at 13:20

user887210

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6 Comments

vacawama Over a year ago

and the preferred way to write Array<Int> is [Int]

user887210 Over a year ago

It's more common to write it as [Int], yes. Although in some rare circumstances Array<Int> does make sense.

Leo Over a year ago

Generic never be nil?

user887210 Over a year ago

If you leave off the ! then it's never nil and it's much safer.

Leo Over a year ago

Thanks, my memory is in swift1.

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