[External] Re: Change to I() in R 4.1

On 10/29/20 23:08, Pages, Herve wrote:
...

I can think of 2 ways to move forward:

1. Keep I()'s current implementation but suppress the warning. We'll
make the necessary adjustments to DataFrame() to repair columns supplied
as I(<S4>) objects. Note that we would still be in the situation where
I(<S4>) objects break validObject() but we've been in that situation for
years and so far we've managed to work around it. However this doesn't
mean that validObject() shouldn't be fixed. Note that print(I(<S4>))
would also need to be fixed (it says "<S4 Type Object>" which is
misleading). Anyways, these 2 issues are separated from the main issue
and can be dealt with later.

1b. A variant of the above could be to use the old implementation for S4
objects only:

  I <- function(x)
  {
      if (isS4(x)) {
          structure(x, class = unique.default(c("AsIs", oldClass(x))))
      } else {
          `class<-`(x, unique.default(c("AsIs", oldClass(x))))
      }
  }

That is probably a good compromise for now.

I would also suggest that the "package" attribute of the S4 class be
kept around so the code that we use to restore the original object has a
way to restore it exactly, including its full class specification. Right
now, and also with the previous implementation, we cannot do that
because attr(class(x), "package") is lost. So something like this:

  I <- function(x)
  {
      if (isS4(x)) {
          x_class <- class(x)
          new_classes <- c("AsIs", x_class)
          attr(new_classes, "package") <- attr(x_class, "package")
          structure(x, class=new_classes)
      } else {
          `class<-`(x, unique.default(c("AsIs", oldClass(x))))
      }
  }

Thanks,
H.