Non-API calls

[lionel-]

Easy:

• SET_ENCLOS(): Used to create new environments, should be easy to fix: Remove SET_ENCLOS() usage rlang#1707
• PREXPR()/R_PromiseExpr()`: Remove PREXPR() usage (as much as we can) rlang#1708

Unknown:

• SET_S4_OBJECT()/UNSET_S4_OBJECT(): Used for proxying / unproxying S4 objects. Can we do better?

Problematic:

• SETLENGTH()/SET_TRUELENGTH(): Used in various algorithms for expansible vectors. Also used in data.table for the same purpose. Would be nice to find a solution with R core.
• STDVEC_DATAPTR(): Part of the ALTREP API. Can we get this part of the experimental API that can be used in packages?

[DavisVaughan]

I think STDVEC_DATAPTR() can be replaced with DATAPTR() but I may be wrong

[MichaelChirico]

Commenting to follow here. @ben-schwen already linked our corresponding issue.

[MichaelChirico]

SET_S4_OBJECT()/UNSET_S4_OBJECT(): Used for proxying / unproxying S4 objects. Can we do better?

Looked at this a little bit. I think we can replace unset_s4() with asS3().

I gave up on r_mark_s4(), the goal would be to handle that with asS4() on the R side.

Alternatively, we might be able to use the C routine asS4() (untested, and not clear we're allowed to use it anyway)?

https://github.com/r-devel/r-svn/blob/main/src/main/objects.c#L1840

[Jean-Romain]

I think STDVEC_DATAPTR() can be replaced with DATAPTR() but I may be wrong

@DavisVaughan tested in my package. It passes all unit tests with no NOTE on devel