warning message for setAs when using class AsIs

[David Kane <David Kane]

This seemed too advanced for r-help and is related to the recent discussion of
character vectors in dataframes.

Following Brian Ripley's most excellent advice, we are moving to a world in
which character vectors in dataframes are always of class AsIs. The cool way of
doing this seemed to be the following:

> cat(c("x", "y", "z"), file = "test.txt", sep = "\n")
> x <- read.table("test.txt")
> class(x$V1)
[1] "factor"

This is what we expect.

> library(methods)
> setAs('character', "AsIs", function(from) I(from))
Warning message: 
Class "AsIs"not defined in: matchSignature(fnames, signature, fdef) 
>

This warning seems wrong to me, although I am not smart enough to follow the
logic through the underlying code. It *seems* as if setAs does not consider
`AsIs' to be an allowed class. However, the desired effect is achieved.

> x <- read.table("test.txt", colClasses=c("AsIs"))
> x
  V1
1  x
2  y
3  z
> class(x$V1)
[1] "AsIs"      "character"
> unlink("test.txt")
> R.version
         _                   
platform sparc-sun-solaris2.6
arch     sparc               
os       solaris2.6          
system   sparc, solaris2.6   
status                       
major    1                   
minor    5.0                 
year     2002                
month    04                  
day      29                  
language R                   
> 

Any comments/suggestions would be much appreciated.

Thanks,

Dave Kane
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