[Rd] How to add a slot to S4 class of an existing package?

[Wolfgang Huber]

Dear Christian

this post from Martin Morgan on class versioning in Bioconductor's 
Biobase package might be relevant:
https://stat.ethz.ch/pipermail/bioc-devel/2006-May/000545.html
and also section 6 of this:
http://www.bioconductor.org/packages/2.4/bioc/vignettes/Biobase/inst/doc/BiobaseDevelopment.pdf

	Best wishes
	Wolfgang

----------------------------------------------------
Wolfgang Huber  EMBL-EBI  http://www.ebi.ac.uk/huber

cstrato wrote:
> Dear all,
> 
> Since my package is based on S4 classes, I would like to know how to add 
> a slot to an existing S4 class without breaking the code of users of my 
> package.
> 
> Assume the following S4 class:
> setClass("MyClass",
>   representation(name = "character",
>                  type = "character",
>                  data = "data.frame"
>   ),
>   prototype(name = "",
>             type = "Default",
>             data = data.frame(matrix(nr=0,nc=0))
>   )
> )#MyClass
> 
> Assume that a user has created an object:
>  > myclass <- new("MyClass", name="MyName", type="MyType", data=tmp)
>  > str(myclass)
> 
> 
> Now I would like to add another slot "info" to MyClass:
> setClass("MyClass",
>   representation(name = "character",
>                  type = "character",
>                  data = "data.frame",
>                  info = "data.frame"
>   ),
>   prototype(name = "",
>             type = "Default",
>             data = data.frame(matrix(nr=0,nc=0)),
>             info = data.frame(matrix(nr=0,nc=0))
>   )
> )#MyClass
> 
> Now when the user loads my package with S4 class MyClass containing a 
> new slot and calls:
>  > str(myclass)
> Error in FUN(c("name", "type", "data", "info")[[4L]], ...) :
>  no slot of name "info" for this object of class "MyClass"
>  >
> 
> My question is:
> Is there any possibility or special trick, which would avoid this error 
> message?
> 
> Are there other possibilities to access an additional data.frame from an 
> existing class?
> 
> Is there something like an "evolution" of S4 classes, which 
> distinguishes the different implementations of an S4 class, and allows 
> the user to keep the object of an old class?
> 
> Best regards
> Christian
> _._._._._._._._._._._._._._._._._._
> C.h.r.i.s.t.i.a.n   S.t.r.a.t.o.w.a
> V.i.e.n.n.a           A.u.s.t.r.i.a
> e.m.a.i.l:        cstrato at aon.at
> _._._._._._._._._._._._._._._._._._
> 
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