[R-pkg-devel] How to make S3-method for the "format" generic for class inheriting from "AsIs"

[Hadley Wickham]

Why not just make your own as.data.frame method? e.g.

as.data.frame.pin <- function(x, ...) {
  structure(
    list(x),
    class = "data.frame",
    row.names = .set_row_names(length(x))
  )
}

data.frame() calls as.data.frame() on all of its arguments.

Hadley

On Tue, Dec 8, 2015 at 5:13 AM, Erik Bulow <erik.bulow at rccvast.se> wrote:
> Dear list!
>
> I am one of two authors to the package "sweidnumbr"
> (https://cran.r-project.org/web/packages/sweidnumbr/index.html). This
> package introduce an S3-class called "pin" and methods etc for handling
> personal identification numbers.
>
> An object might look like:
> x <- structure("1912121212", class = c("AsIs", "pin", "character"))
>
> We want the "AsIs" class to allow for example recycling when the object is
> put into a data.frame. Problem is that we would also like to have our own
> format.pin-method. This is problematic since base::format.AsIs does not
> use "NextMethod" (which all other xxx.AsIs methods do).
>
> We can think of two possible solutions:
>
> 1. We can redefine the format-function to handle this but will then get a
> check note for masking base::format.
> 2. We could skip the format.pin method and introduce a stand alone
> function called "pin_format" or similair (but our method is very similair
> to base::format.Date and we would like to benefit from that).
>
> We can not skip the "AsIs" class inheritence. If we do, we need to rewrite
> "data.frame" (which is a function and not an S3 generic in opposite to
> as.data.frame for which we could just add as.data.frame.pin). If we do, we
> still get the same check note as above but for masking base::data.frame
> instead.
>
> Is it possible to use both the benefits of the AsIs-class but to also
> define our own format-method without masking anything from other packages?
>
> Best regards
> Erik Bülow
>
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