[Rd] Defining a `show` function breaks the print-ing of S4 object -- bug or expected?

Dean Attali daattali at gmail.com
Tue Jun 30 09:02:34 CEST 2015

Hi r-devel

If you define a function named `show` or attach a package with an exported
`show` function, then printing/vieweing S4 objects breaks. This is probably
because the `print` function calls `show`, which is now masked.


show <- function() {}
> setClass("Person", slots = list(name = "character"))
> tom <- new("Person", name = "Tom")
> tom # error
> methods::show(tom) # works

The error was a surprise to me because  I was under the assumption that
`show` would be namespaced and therefore should not break.
I'm wondering if this is intended behaviour, or if this is a problem.  My
intuition, and Hadley agreed on Twitter, is that defining a `show` method
should not have such a grave effect on printing S4 objects.



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