GDScript 2.0: Packed arrays are not considered constant expressions

[dalexeev]

Godot version

v4.0.beta3.official [01ae26d31]

System information

Kubuntu 22.10

Issue description

Attempting to use a packed array in a constant definition causes "Initializer for a constant must be a constant expression" error.

Steps to reproduce

# 3.x:
const A = PoolIntArray() # OK.
const B = PoolIntArray([1, 2, 3]) # OK.

# 4.0-dev:
const A = PackedInt32Array() # Error: Initializer for a constant must be a constant expression.
const B = PackedInt32Array([1, 2, 3]) # Error: Initializer for a constant must be a constant expression.

Minimal reproduction project

No response

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See also:

• godotengine/godot-proposals#5653

[rune-scape]

related to https://github.com/godotengine/godot/issues/66949 introduced in https://github.com/godotengine/godot/commit/a604e72dc974723439e9df5edc67502b82beba4b

[dalexeev]

Also, we should not forget about readonly Packed*Arrays (make_read_only()), for consistency with Array and Dictionary.

[vnen]

Also, we should not forget about readonly Packed*Arrays (make_read_only()), for consistency with Array and Dictionary.

This might be tricky because Packed*Array are just typedefs for Vector<>. Adding read-only functionality would affect all vectors used in core.

They could be made proper classes inheriting from Vector<> and adding features, but that's a big change and should be discussed on its own merit.

[dalexeev]

This might be tricky because Packed*Array are just typedefs for Vector<>. Adding read-only functionality would affect all vectors used in core.

Yes, I was worried about it, and that's why I tried to draw attention to it yesterday. :)

[dalexeev]

I suggest deferring this to 4.2 or 4.x as 4.1 is in a feature freeze. Since this is more a lack of a new feature than a bug. Packed arrays have changed significantly in 4.0, they are now passed by reference rather than by value. And since they don't have a make_read_only() method (unlike Array and Dictionary), we can't make them constant as it worked before on the GDScript side. Core changes are required, and now is not the time to experiment with such important engine structure as Vector<T>. Please add the topic:core label.