[Rd] Change to I() in R 4.1

[Pages, Herve]

Hi there,

Is that change in R-devel intentional?

   library(Matrix)
   m <- as(matrix(c(0, 1)), "sparseMatrix")

   isS4(m)
   # [1] TRUE

   x <- I(m)
   # Warning message:
   # In `class<-`(x, unique.default(c("AsIs", oldClass(x)))) :
   #   Setting class(x) to multiple strings ("AsIs", "dgCMatrix", ...); 
result will no longer be an S4 object

   isS4(x)
   # [1] FALSE

This works fine in R 4.0.3 i.e. no warning and I() doesn't turn off the 
S4 bit of the object.

This change breaks 17 Bioconductor packages.

Seems that the culprit is this change in how I() is implemented:

In R 4.0.3:

   > I
   function (x)
   {
     structure(x, class = unique(c("AsIs", oldClass(x))))
   }

In R devel:

   > I
   function (x)
   `class<-`(x, unique.default(c("AsIs", oldClass(x))))

Unfortunately there is a bunch of code around that calls I() on S4 
objects, admittedly not necessarily for very good reasons, but it 
happens. Would it be possible that I() has a less destructive effect on 
S4 objects?

Thanks,
H.

 > sessionInfo()
R Under development (unstable) (2020-10-17 r79346)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 20.04.1 LTS

Matrix products: default
BLAS:   /home/biocbuild/bbs-3.13-bioc/R/lib/libRblas.so
LAPACK: /home/biocbuild/bbs-3.13-bioc/R/lib/libRlapack.so

locale:
  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
  [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] Matrix_1.2-18

loaded via a namespace (and not attached):
[1] compiler_4.1.0  grid_4.1.0      lattice_0.20-41

-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
P.O. Box 19024
Seattle, WA 98109-1024

E-mail: hpages using fredhutch.org
Phone:  (206) 667-5791
Fax:    (206) 667-1319