##  FALSE
This should return TRUE, since is.na.data.frame is the S3 method of is.na for data.frame objects, as seen by
##  is.na.POSIXlt is.na.data.frame is.na.numeric_version is.na.raster*
## see '?methods' for accessing help and source code
and documented on the ?is.na help page.
Created attachment 2174 [details]
suggested fix for isS3method
I've attached a possible fix for isS3method that loops over all choices of generic/class combinations. For example, with "is.na.data.frame" as the input, it would check
fn = "is" and class = "na.data.frame"
fn = "is.na" and class = "data.frame"
fn = "is.na.data" and class = "frame"
Thank you, Richie.
Your suggestion is good "in spirit" but has too many changes compared to the source.
My fix uses the (same ?) approach : look at all possible cases and return (TRUE) immediately if one case "works".
I may not get to commit my fix by tomorrow,
but there's no need for more proposals.
Committed the fix r71618 | maechler | 2016-11-03 12:48:47 +0100 (to R-devel)
and ported to 'R 3.3.2 patched'.