R devel - Jun 2011 - S4 class, passing argument names to function, modify original

Hello, an S4 class "Foo" is defined with a setter, $. For several
reasons, the setter calls a function, .foo.update(). However, bypassing the
argument names of the setter does not work. Question 1: Why not and how can I
fix this? Question 2: What is the way to define either the function or the
setter to modify the original object (not returning the modified copy of it an
overwrite the original by assignment)? Thanks, S?ren

setClass("Foo",
  representation(
    N = "numeric"
  ),
  prototype(
    N = 10000
  )
)

.foo.update <- function(object, ...) {
  args <- list(...)
  for (i in slotNames("Foo")[pmatch(names(args),
slotNames("Foo"), nomatch=0)]) {
    slot(object, i) <- args[[i]]
    # indeed more to do here
    return(object)
  }
}

setReplaceMethod("$", "Foo",
  function(x, name, value) {
    x <- .foo.update(x, name=value)
    x
  }
)

x <- new("Foo")
x
x$N <- 99
x # NULL????

On 06/04/2011 03:07 AM, soeren.vogel at uzh.ch wrote:
> Hello, an S4 class "Foo" is defined with a setter, $. For several
reasons, the setter calls a function, .foo.update(). However, bypassing the
argument names of the setter does not work. Question 1: Why not and how can I
fix this? Question 2: What is the way to define either the function or the
setter to modify the original object (not returning the modified copy of it an
overwrite the original by assignment)? Thanks, S?ren
>
> setClass("Foo",
>    representation(
>      N = "numeric"
>    ),
>    prototype(
>      N = 10000
>    )
> )
>
> .foo.update<- function(object, ...) {
>    args<- list(...)
>    for (i in slotNames("Foo")[pmatch(names(args),
slotNames("Foo"), nomatch=0)]) {
>      slot(object, i)<- args[[i]]
>      # indeed more to do here
>      return(object)
>    }
> }
Since names(args) is 'name', and 'name' is not a slot of
'Foo', the
return of pmatch is 0 and .foo.update returns NULL. Put return(object) 
outside the for loop.
> setReplaceMethod("$", "Foo",
>    function(x, name, value) {
>      x<- .foo.update(x, name=value)
here your intention is that name=value to be substituted with N=99, but 
you end up with name=99. You could arrange to parse this correctly, but 
this isn't usually what you _want_ to do and I don't really understand 
what you're trying to accomplish. Maybe

.foo.update <- function(object, name, value, ...)
{
     slot(object, name) <- value
     ## some other stuff
     object
}

Hope that helps a bit.

Martin
>      x
>    }
> )
>
> x<- new("Foo")
> x
> x$N<- 99
> x # NULL????
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

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