[R] overloading the generic primitive functions "+" and "["

[Barry Rowlingson]

On Thu, Oct 28, 2010 at 2:12 PM, Martin Morgan <mtmorgan at fhcrc.org> wrote:

> Not so hard, eh? Though then like your S3 implementation this makes all
> 'Ops' (see ?Ops)

 Except you have to re-run the set* things every R session:

 > setClass("SS", "character")
 > setMethod(Ops, c("SS", "SS"), function(e1, e2) paste(e1, e2))
 > a=new("SS","hello")
 > b=new("SS","world")
 > a+b
 [1] "hello world"
 > q()
 Save workspace image? [y/n/c]: y

...start R again...

[Previously saved workspace restored]

 > a=new("SS","hello")
 > b=new("SS","world")
 > a+b
 Error in a + b : non-numeric argument to binary operator

 It seems the SS class is preserved but the method definition isn't.
Otherwise new("SS","hello") fails.

 That's one of the things that confuses me about S4 - its use of
invisible global things. ls(all.names=TRUE) shows me the bits:

 > ls(all.names=TRUE)
 [1] "a"                      ".__C__SS"               ".requireCachedGenerics"

 It seems that .__C__SS is the class definition, and the
.requireCachedGenerics seems to imply I've done something with 'Ops':

 > .requireCachedGenerics
[[1]]
[1] "Ops"

 but doesn't actually store and restore my definition.

 A bug? I dunno. Version 2.10.1 if anyone cares. I don't. I'll just go
back to my S3 method which is just as simple and works when I restore
the .RData I saved things to. Each to their own!


Barry