[Rd] as.POSIX{ct,lt} fail on class "AsIs"

[Don MacQueen]

(I think this is probably appropriate for r-devel -- if my diagnosis 
is correct, that is)

I have a script that I run infrequently (i.e., quarterly) that has 
been working for several years. I re-ran it this morning for the 
first time since updating R from 2.6.2 to 2.7.0, and encountered an 
error.

I found a simple example that shows the problem:

>  as.POSIXct( I( '2008-01-01' ) )
Error in as.POSIXlt.default(x, tz, ...) :
   do not know how to convert 'x' to class "POSIXlt"
>
>  traceback()
6: stop(gettextf("do not know how to convert '%s' to class \"POSIXlt\"",
        deparse(substitute(x))))
5: as.POSIXlt.default(x, tz, ...)
4: as.POSIXlt(x, tz, ...)
3: as.POSIXct(as.POSIXlt(x, tz, ...), tz, ...)
2: as.POSIXct.default(I("2008-01-01"))
1: as.POSIXct(I("2008-01-01"))

>  class( I('2008-01-01') )
[1] "AsIs"
>  is.character( I('2008-01-01') )
[1] TRUE

It looks to me as though as.POSIXlt() does not recognize the object 
as being also a character object
because it calls as.POSIXlt.default() instead of as.POSIXlt.character().


>  sessionInfo()
R version 2.7.0 (2008-04-22)
powerpc-apple-darwin8.10.1

locale:
C

attached base packages:
[1] utils     stats     graphics  grDevices methods   base


I have done some searching in r-help, r-devel, and NEWS through 2.8 
Series News and not found anything that I recognized as either a fix 
or an indication this is intended behavior.  (Doesn't mean it isn't 
there, of course...)

By way of background, I sometimes use the class "AsIs" for the reason 
described in?AsIs, i.e.,
      "Protecting an object by enclosing it in 'I()' in a call to 
'data.frame' inhibits the conversion of character vectors to 
factors..."
and that's what led to this discovery.

Thanks
-Don
-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062