>>>>> Michael Chirico
>>>>> on Thu, 5 Mar 2026 14:26:16 -0800 writes:
> I found myself needing to add methods::setOldClass("difftime") in
> order to also set a coercion method for my class to difftime:
> methods::setAs("myClass", "difftime", ...)
> And thus avoid the on-load message:
> in method for ‘coerce’ with signature ‘"myClass","difftime"’: no
> definition for class “difftime”
> I see 10 or so other packages also doing the same [1].
> I am wondering, though, since {base} owns this class, if it shouldn't
> be registered already? I see inclusions for, e.g., closely-related S3
> classes Date and POSIXt [2].
In my vague recollection "difftime" came a bit later than "Date"
and "POSIXlt". This may be the reason for its non-presence.
> OTOH, I see .OldClassesList hasn't really been edited in 15+ years, so
> maybe this approach has lost favor and is better not amended anymore
> [3].
well, favors related to S4 have always been somewhat segregated ..
> (or maybe this is really an r-package-devel question about whether
> supporting as(<my class>, "difftime") is actually beneficial...)
The use of as(., <...>) is an R-help question really not
restricted to package development at all.
I agree that "difftime" does naturally belong alongside "POSIXt"
and I am happy to add it to the list;
(I did check to see if an unneeded setOldClass(<already_set>)
gives a warning, and it doesn't)
Martin
> Mike C
> [1]
https://github.com/search?q=org%3Acran%20%2FsetOldClass.*difftime%2F&type=code
> [2]
https://github.com/r-devel/r-svn/blob/b7850c8cae0956592019c5f8f59e885d3d39ae6f/src/library/methods/R/BasicClasses.R#L550-L552
> [3]
https://github.com/r-devel/r-svn/blame/b7850c8cae0956592019c5f8f59e885d3d39ae6f/src/library/methods/R/BasicClasses.R#L541-L569
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