[R] "a"+"b"

[Prof Brian Ripley]

Not easily.  There's a comment in ?Ops that for efficiency the group 
generics only dispatch on objects with a "class" attribute: otherwise you 
could use an S3 method like

`+.character` <- function(e1, e2) paste(e1,e2, sep="")

S4 methods are built on top of S3 methods as far as internal dispatch is 
concerned, so the same comment will apply there AFAICS.

I would think that the intention was also to positively discourage messing 
with the basics of R, as if you were able to do this erroneous uses would 
likely not get caught.

On Tue, 2 May 2006, Matthew Dowle wrote:

>
> Hi,
>
> Is there a way to define "+" so that "a"+"b" returns "ab" ?
>
>> setMethod("+",c("character","character"),paste)
> Error in setMethod("+", c("character", "character"), paste) :
>        the method for function '+' and signature e1="character",
> e2="character" is sealed and cannot be re-defined
>> "a"+"b"
> Error in "a" + "b" : non-numeric argument to binary operator
>
> Thanks!
>
>
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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