Filled array with array iterates "wrongly".

[PeterMarques]

Tested versions

3.5.3

System information

editor

Issue description

When running:

extends Node

func _ready():
	var a = []
	
	a.resize(3)
	a.fill([])
	
	for each in a.size():
		a[each].append(randi())
		
	print(a)
	
	var b = []
	b.resize(3)
	
	for each in b.size():
		b[each] = []
		b[each].append(randi())
		
	print(b)

you get:

[[3161026589, 2668139190, 4134715227], [3161026589, 2668139190, 4134715227], [3161026589, 2668139190, 4134715227]]
[[4204663500], [1099556929], [3154986942]]

It seens that both outputs must be like the second one.

The first case is iterating again inside the branches, and copying the values.

Or i am missing something? i tried using fill([].duplicate()) but same behaviour.

Steps to reproduce

run the code

Minimal reproduction project (MRP)

Bug Array.zip

[dalexeev]

a.fill([])

Arrays are passed by reference, you fill the outer array with a reference to the same array. This is already documented:

Note: If value is of a reference type (Object-derived, Array, Dictionary, etc.) then the array is filled with the references to the same object, i.e. no duplicates are created.

We could solve this by adding optional parameters duplicate = false and deep = false.

[PeterMarques]

a.fill([])

We could solve this by adding optional parameters duplicate = false and deep = false.

and

[...] has been solved in 4.x I][...]

changing to a.fill([].duplicate(false)) still produces the same output, even on 4.3dev5

[dalexeev]

changing to a.fill([].duplicate(false)) still produces the same output, even on 4.3dev5

This shouldn't change anything. You create the array once, make a duplicate once, and pass the duplicate to fill(), which fills the entire outer array with the same reference, as the documentation says. To create N different arrays you need to use a loop.

In other words, the expression [].duplicate(false) is evaluated only once. You pass to fill() method the expression value, not the expression itself.

[AThousandShips]

(note the outdated hidden comment, I got this confused with another bug related to shared literals)

[PeterMarques]

So, the patterns are NOT and SHOULD NOT be equivalent?

Ok, so there is NO WAY to fill a array with a blank arrays using fill() and one need to use the iterator to alocate/or push the blank non referenced arrays inside it, and this is the only way to do that?

If so, ok, no more to discuss, but i, nonetheless, find it odd.

Will just stick to iterate it fully and forget about the fill, and maybe even the resize, on that use case.

Thanks.

[dalexeev]

So, the patterns are NOT and SHOULD NOT be equivalent?

Yes, they shouldn't.

We could solve this by adding optional parameters duplicate = false and deep = false.

I think this should be opened as a proposal instead, if you're interested. However, the current behavior appears to be correct as is: fill() is intended to fill an array with identical elements. Arrays that are value-equal but not reference-value probably cannot be considered the same (see also is_same()).

Given the above, let's close this issue, since the behavior is not a bug and is correctly documented. Thanks for the contribution nonetheless!