How to call a function with an `inout` argument on each element of array?

Question

I have a function which takes inout argument

 func modify(word: inout Word)

I need to call it on each element of array. Here is what I do

for word in words {
    modify(word: &word)
}

But I get error:

cannot pass immutable value as inout argument: 'word' is a 'let' constant

I tried to iterate through map words.map{ modify(word:&$0) }, still the same error:

cannot pass immutable value as inout argument: '0$' is immutable

Is there any way to call a function with an inout argument on each element of array?

Don't use inout. If you must then you will need to iterate over the array, building a new array with the modified words or use an index variable rather than enumeration — Paulw11
– Paulw11, Commented Dec 1, 2016 at 21:31

infinisil · Accepted Answer · 2016-12-01 21:53:30Z

1

When using the for word in words syntax, word is actually an immutable copy of the element in the array.

To modify the array directly, iterate over the indices instead:

for i in words.indices {
    modify(word: &words[i])
}

which is equivalent to (for arrays at least)

for i in 0..<words.count {
    modify(word: &words[i])
}

answered Dec 1, 2016 at 21:53

infinisil

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2 Comments

Deleting my answer after seeing your's. I never knew this and posted a less "Swifty" version of your answer! Nice!

Note that words still needs to be declared with var, not let.