Const expressions of equal value and type are shared

[cdemirer]

Godot version

4.0.dev (28174d5)

System information

5.15.2-2-MANJARO

Issue description

I couldn't find any open issue about this behavior of const. const initializer expressions that reduce to the same type and same (==) value are shared, as an optimization I assume. But this can lead to unexpected situations.

According to the docs, const arrays are intended to be mutable. This is fine by itself, but with the sharing behavior, it is chaos:

const arr1 = []
const arr2 = []
func _ready():
    arr1.append(1)
    print(arr1)
    print(arr2)

Output:

[1]
[1]

Note: This is not only for empty arrays.

I believe another issue, brought up by @aaronfranke on rocket chat, is caused by the same behavior:

print(0.0)
print(-0.0)

0.0
0.0

and:

print(-0.0)
print(0.0)

-0.0
-0.0

Steps to reproduce

Just run the code blocks in "Issue description".

Minimal reproduction project

No response

[Calinou]

I can confirm this on master 28174d5.

This does not occur on 3.5.beta (a75afd6), so this is a regression in the new GDScript implementation in master.
On 3.x, I get:

[1]
[]

PS: For correct syntax highlighting, code blocks should use gdscript as a language, not gd. I edited your comment accordingly 🙂

[aaronfranke]

I think the solution here is to ensure the bits are equal instead of checking that == is true. For arrays this would mean checking that the references are equal or different, for floats it would mean that 0.0 and -0.0 are both saved as different values. Also, for floats, I'd guess that NaN values are currently saving multiple copies when one would work since == is always false with NaN.