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Start your free trialManish Giri
16,266 PointsAre function parameters immutable in Swift?
I was playing around with the code from the function scope video, and I got an errorr with this code -
var testArray: [Int] = [1,2,3,4,5]
func arrayModifier(arr: [Int]) -> [Int] {
/*
var firstArr = arr
firstArr.append(10)
print("FirstArr = \(firstArr)")
*/
arr.append(10)
var secondArr = arr
return secondArr
}
var resultArr = arrayModifier(arr: testArray)
The commented out part works fine(as in the video), but when I try to append a value to the function parameter arr, it failed. Here's the error -
Playground execution failed: error: Swift-Functions.playground:100:5: error: cannot use mutating member on immutable value: 'arr' is a 'let' constant
arr.append(10)
^~~
Does it mean that you cannot modify function parameters at all in Swift? Or is it only applicable to certain data types. Coming from a Java/JS background, this seems confusing.
Thanks!
Alex Koumparos
Python Development Techdegree Student 36,887 PointsAlex Koumparos
Python Development Techdegree Student 36,887 PointsHi Manish,
Yes, function parameters are immutable in Swift (at least, as of Swift 3).
If you want to create a mutable value scoped to the function then declare a new variable equal to the parameter's value. If you want to a make the input parameter mutable and have the same scope as the input variable (so that changes in the function alter the value that was passed in when calling the function), then you can declare that parameter as
inout
.Here is a link to Apple's documentation on inout: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Functions.html