In x$name, 'name' is supposed to be a symbol, unevaluated, or a
literal character string (but not a character vector).
> f <- list(bob=1, alice=2)
> `$`(f, "bob")
[1] 1
> nm <- "bob"
> `$`(f, nm)
NULL
illustrates your misunderstanding.
Note that the S4 generic for $ in fact is
"$" = function(x, name)
{
name <- as.character(substitute(name))
standardGeneric("$")
}
so within S4 dispatch you will have a character vector for 'name'.
You need substitute() to get back to a literal character string.
I think the latter should be documented somewhere, but like many details
of S4, it is not AFAIK.
On Mon, 7 May 2007, Seth Falcon wrote:
> Hello,
>
> I wonder if this will make it through the spam filters given the
> subject line.
>
> I'm seeing the following when trying to call a dollar method inside of
> a dollar method.
>
>
> setClass("Foo", representation(d="list"))
> [1] "Foo"
>
> f <- new("Foo", d=list(bob=1, alice=2))
>
> ## We can call dollar at this level and it works as expected
>
> `$`(f, "bo")
> [1] 1
>
> `$`(f, "al")
> [1] 2
>
> ## So set a method on Foo that does this
>
> setMethod("$", "Foo", function(x, name) `$`([EMAIL PROTECTED], name))
> [1] "$"
>
> ## But it doesn't work. Why?
>
> f$bo
> NULL
>
> f$al
> NULL
>
> ## Here is a hackish workaround.
>
> setMethod("$", "Foo", function(x, name)
> eval(substitute([EMAIL PROTECTED], list(FOO=name))))
> [1] "$"
>
> f$bo
> [1] 1
>
> f$al
> [1] 2
>
> Other suggestions for workarounds? Is this a bug?
>
> + seth
>
>
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
