Cannot pass references to functions and use them properly

[qwertfisch]

Hello!
I’m quite new to V and have a problem concerning iterating over a recursive list structure. That is, iterating works in the same function where the structure is defined, but I cannot create a mutable reference that just points to any inner list using a function.

Here is the definition of the structure and the working code:

[heap]
struct ValueList {
	mut:
	values []Value
}
type Value = ValueList | int

fn main() {
	mut list := ValueList{}
	list.values << 1
	list.values << ValueList { values: [Value(11), Value(12)] }

	mut last_value := &list
	for {
		if last_value.values.len > 0 && last_value.values.last() is ValueList {
			last_value = &(last_value.values.last() as ValueList)
		} else {
			break
		}
	}
	last_value.values << 13
	println(last_value)
	println(list)
}

The function in the for loop should iterate over the ValueList, get the last element, and if it’s another list, recursively find the next last element of this list, and so on. It doesn’t matter exactly what it does. The point is, the reference last_value is updated, and in the last lines you can see, I add an element to the last list, and the complete list is also updated. Works as intended.

But when I want to move the code into a function, the same thing works differently.

fn get_last(mut last_value &ValueList) &ValueList {
	for {
		if last_value.values.len > 0 && last_value.values.last() is ValueList {
			last_value = &(last_value.values.last() as ValueList)
		} else {
			break
		}
	}
	return last_value
}

I still get a reference to the element I wanted to find, but it also changes the complete list. This can be seen with this added code to the main function:

	mut last_value2 := get_last(mut &list)
	println(last_value2)
	println(list)

Question

So the question is: How can I move the code from the main function into another function? How can I pass a mutable reference, and changing this reference only changes the reference and not the referenced value?

Another strange behaviour

Also, when testing around with other implementation variants, I discovered this very strange behaviour:

fn get_last(mut list &ValueList) &ValueList {
	mut last_element := list // Why is the type ValueList instead of &ValueList?
	// ... here would be could to return the innermost list ...

	return &last_element
}

If I copy the reference (here the function parameter list), I still get value type, not a reference! Why?
And changing values based on the copied and/or returned reference would then only change a duplicate of the complete structure, and that is quite useless, because I passed a reference to just not create any duplicates.