Does range operator really copy the iterable?

[lootek]

Hello, first of all, please accept many thanks for the great book you wrote! It's awesome to have all those gotchas collected in one place and so well explained :)

I would like to ask for a further explanation of the statement in the book that made me a bit confused though. It says that the range operator copies the slice/array/channel being iterated over (ie the range clause) on its first (and only) evaluation just before the iteration. I cannot find that in the relevant part of the Golang spec. My understanding was, on the other hand, the for-range behaves that way because it's the v (the local iterator variable) that is a copy of the slice element (not that the whole iterable thing gets copied). Please see the following snippet: https://go.dev/play/p/tEE8fW6Jxrk.

Referring to the code samples in this repo here, such a statement can be found in the book as the comment eg. to this one (or a couple of other snippets in the 4.2.x chapter):

100-go-mistakes/04-control-structures/31-range-loop-arg-evaluation/arrays/main.go

Lines 5 to 13 in b2152d0

	func listing1() {
	a := [3]int{0, 1, 2}
	for i, v := range a {
	a[2] = 10
	if i == 2 {
	fmt.Println(v)
	}
	}
	}

[teivah]

You are right; this could be better phrased. Thanks, it'll be updated in the next version.