Support OBJSXP coming in R 4.4.0 (closes #1283)

[eddelbuettel]

This addressed #1283 and the addition of OBJSXP as a new value / replacement for S4SXP to better support S7 changes. I ran a full reverse-depends check but given that the change is conditional on R 4.4.0 or later nothing much came up.

It is something we probably want to get into 1.0.12 for the next cycle. and I don't think it will do anything wrong but reviews would be much appreciated as I may still have forgotten something.

• Code compiles correctly
• R CMD check still passes all tests
• Preferably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[Enchufa2]

I think we still want to return S4SXP in the appropriate cases. So following this, in case OBJSXP,

• if (IS_S4_OBJECT(x)) return "S4SXP";
• otherwise, return "OBJSXP";

EDIT: Maybe Rf_isS4 instead of IS_S4_OBJECT?

[eddelbuettel]

I like that a lot. So how about

#if R_Version >= R_Version(4,4,0)					// replaces S4SXP in R 4.4.0
        case OBJSXP:    	return Rf_isS4(x) ? "S4SXP" : "OBJSXP"; 	// cf src/main/inspect.c
#else
        case S4SXP:     	return "S4SXP";
#endif

moving the switch inside the 'after R 4.4.0' conditional and returning 'S4SXP' for S4 as before and 'OBJSXP' otherwise.

[Enchufa2]

Perfect!

[eddelbuettel]

Even seems to work:

> library(Rcpp)
> M <- Matrix::rsparsematrix(2,2,0.5)
> cppFunction("const char* t(SEXP x) { return type2name(x); }")
> t(1L)
[1] "INTSXP"
> t(M)
[1] "S4SXP"
> getRversion()
[1] ‘4.4.0’
> 

And now I get to learn how to create an S7 object :)

Edit: No luck. All I get is CLOSXP but I chalk that up to the S7 package rather than the diff here.

[Enchufa2]

LGTM!