Use R C API compliant S4 utilities #2084
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DavisVaughan
commented
Oct 23, 2025
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| static inline SEXP r_mark_s4(SEXP x) { | ||
| SET_S4_OBJECT(x); | ||
| return(x); | ||
| static inline bool r_is_s4(SEXP x) { | ||
| return Rf_isS4(x); | ||
| } | ||
| static inline SEXP r_unmark_s4(SEXP x) { | ||
| UNSET_S4_OBJECT(x); | ||
| return(x); | ||
| static inline SEXP r_as_s4(SEXP x) { | ||
| // - Return value must be used, unlike `SET_S4_OBJECT()` | ||
| // - `Rf_asS4()` calls `shallow_duplicate(x)` if `MAYBE_SHARED(x)` | ||
| // - `flag = 1` goes through `SET_S4_OBJECT()` | ||
| // - `complete` is never utilized when `flag = 1` | ||
| const Rboolean flag = 1; | ||
| const int complete = 0; | ||
| return Rf_asS4(x, flag, complete); | ||
| } | ||
| static inline SEXP r_as_not_s4(SEXP x) { | ||
| // - Return value must be used, unlike `UNSET_S4_OBJECT()` | ||
| // - `Rf_asS4()` calls `shallow_duplicate(x)` if `MAYBE_SHARED(x)` | ||
| // - `flag = 0` goes through `UNSET_S4_OBJECT()` | ||
| // - `complete` is for S4 objects that wrap a "complete" S3 object by placing | ||
| // it in the `.Data` slot. If you set `complete = 1`, it will unwrap and | ||
| // return that, which we don't want. If `complete = 0`, no additional | ||
| // behavior will happen beyond the `UNSET_S4_OBJECT()` call. | ||
| const Rboolean flag = 0; | ||
| const int complete = 0; | ||
| return Rf_asS4(x, flag, complete); | ||
| } |
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Here is the family of 3 S4 utilities we need
The main points are:
- These are no longer "mark" functions. The return value actually does matter. I have updated the names and call sites accordingly.
Rf_asS4(), used for both setting and unsetting the S4 bit, will shallow clonexif it is shared. Where we use it invec_restore_default()we have freshly clonedxalready withvec_clone_referenced(x, ownership)so it should not look shared unless we providedVCTRS_OWNERSHIP_deepandxwas somehow shared already, even though we claimed to own it completely. There is nothing we can do about this since we don't have access toSET_S4_OBJECT()now. I don't know how common this would be.completeis not anything we need to worry about, we just set it to0and it is never used.
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| if (is_s4) { | ||
| r_mark_s4(x); | ||
| x = r_as_s4(x); |
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Not protecting because we are on the way out here
lionel-
approved these changes
Oct 24, 2025
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Part of #1933
Closes #1940
Uses
Rf_isS4()andRf_asS4()fromhttps://github.com/wch/r-source/blob/8d57e7515089387414c75df502f3f0c0e2c022e5/src/main/objects.c#L1838-L1878
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