feat: unbox_snapshot to unbox Box<T> into @T

[enitrat]

Feature Request

Describe the Feature Request

A libfunc/corelib function to unbox a Box<T> type into a @T type. This would allow us to not take ownership of the value inside the box when unboxing it, and would avoid unnecessary unbox-rebox operations when accessing a field of the T type without modifying it.

Describe Preferred Solution

A libfunc similar to match_nullable_snapshot - that converts a Box<T> to a @T.

Describe Alternatives

Related Code

Additional Context

If the feature request is approved, would you be willing to submit a PR?
(Help can be provided if you need assistance submitting a PR)

I can try myself at it with some guidance

• Yes
• No

[orizi]

I think instead adding a: extern fn box_forward_snapshot<T>(value: @Box<T>) -> Box<@T>; would be better (less actual logic).
same for: extern fn nullable_forward_snapshot<T>(value: @Nullable<T>) -> Nullable<@T>; - this can probably replace match_nullable_snapshot as well.
I'm wondering if having the opposite as well would be beneficial.

[enitrat]

I think instead adding a: extern fn box_forward_snapshot(value: @box) -> Box<@t>; would be better (less actual logic).

Sounds good!

I'm wondering if having the opposite as well would be beneficial.

I don't see any specific use case for this. Do you mean @T into Box<T>?

[orizi]

no - just instead of forwarding the snapshot pulling it backwards - i indeed don't see a particular usecase.