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
>
`$`([EMAIL PROTECTED], "bo"), surely.
> ## So set a method on Foo that does this
>
> setMethod("$", "Foo", function(x, name) `$`([EMAIL PROTECTED], name))
> [1] "$"
>
> ## But it doesn't work. Why?
>
>
This has nothing to do with methods, it's $'s nonstandard evaluation
rules that are doing you in. This doesn't work either
> x <- "al"
> `$`([EMAIL PROTECTED], x)
NULL
and the reason is that `$`(a,b) is _exactly_ equivalent to a$b insofar
as auto-quoting the second argument is concerned
> f$bo
> NULL
>
> f$al
> NULL
>
>
...so both of these look for [EMAIL PROTECTED] which isn't there.
> ## 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?
>
Not a bug. Another workaround is to use "[[", but beware that Robert has
evil intentions with respect to that and partial matching...
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