How can we write to a parameter-pack tuple with the iteration syntax?

Using Swift
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func myFunction<each T: FixedWidthInteger>(_ t: repeat each T) -> (repeat each T) { for value in repeat each t { print(value) } var result = (repeat each t) for dummy in repeat each ??? { // `result`, or `&result`, is in the ??? dummy += 1 } return result }

How can I write to each member of result one at a time? (I can't use an all-at-once functional solution here.) The actual needs are more complicated, but I need to work with the above first before asking new questions.

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I think for now you're limited to an all-at-once functional solution.

It's not obvious from documentation, but you can call function on each element. In example below, I map simple { $0 + 1 } closure on each member of tuple.

Maybe something like this could meet your needs.

func myFunction<each T: FixedWidthInteger>(_ t: repeat each T) -> (repeat each T) { return (repeat { $0 + 1 }(each t) ) } // Prints: // (2, 3, 4, 5) let result = myFunction(1, 2, 3, 4) print(result)
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Unfortunately we don't have a way to actually mutate or initialize packs like that yet.

You can always use the "functional solution" actually, if you extract the body of your for loop into a local function foo() that returns the new value, and then you can do var result = (repeat foo(each t)) to form the result.