A compilation error is thrown after compiling the Custom Iterators example in the For Loop documentation

[ookami-001]

A compilation error is thrown after compiling the Custom Iterators example in the For Loop documentation

[JalonSolov]

Your code does not match the docs, since you have wrapped most of it inside a fn main.

The next() function must be outside main, as it's own function, for this to work.

If you look more closely at the docs, you'll see there's no main at all - it is not needed, as this is an example of "script mode" V.

[ookami-001]

You are right. After I changed the contents of the main.v file to the following:

module main

struct SquareIterator {
	arr []int
mut:
	idx int
}

fn (mut iter SquareIterator) next() ?int {
	if iter.idx >= iter.arr.len {
		return none
	}
	defer {
		iter.idx++
	}
	return iter.arr[iter.idx] * iter.arr[iter.idx]
}

fn main() {

	nums := [1, 2, 3, 4, 5]
	
	iter := SquareIterator{
		arr: nums
	}

	for squared in iter {
		println(squared)
	}
	
}

the code compiled successfully and produced the expected outcome:

1
4
9
16
25

Still, I feel that this will catch many new learners off guard as many will probably do exactly as I did by including the next() function inside the main() function. I strongly think that example in the documentation needs to be edited to look like the code I posted above to avoid potential confusion from new learners. The more people who fall in love with V the better and clearer documentation is one way of achieving that.

I will look out for more issues like this as I continue my learning of V.

[JalonSolov]

The proper edit to add the main function would be

module main

struct SquareIterator {
	arr []int
mut:
	idx int
}

fn (mut iter SquareIterator) next() ?int {
	if iter.idx >= iter.arr.len {
		return none
	}
	defer {
		iter.idx++
	}
	return iter.arr[iter.idx] * iter.arr[iter.idx]
}

fn main() {
	nums := [1, 2, 3, 4, 5]
	
	iter := SquareIterator{
		arr: nums
	}

	for squared in iter {
		println(squared)
	}
}

as V doesn't allow you to wrap a named function inside another function (hence the error message you received):

error: unexpected token `(` after anonymous function signature, expecting `{`

Only anonymous functions can be declared inside other functions.

It's a toss-up whether this would make a difference... may people would likely try running the example as-is, rather than adding to it, just to see what it would do.