Bug in new() or validObject() in methods package (PR#7922)

The bug might be here:

is.null(expression())

[1] TRUE

But

is.null(expression(NULL))

[1] FALSE

So it might look to the methods package like you're passing in a NULL
value for @bar. I might argue that expression() should not be NULL (and
only NULL is NULL) as I have had similar trouble trying to extend
language objects to S4 classes, partially because length 0 name, call
and expression objects are either not available, or in this case,
handled poorly.

Robert

-----Original Message-----
From: Duncan Murdoch [mailto:murdoch@stats.uwo.ca] 
Sent: Monday, June 06, 2005 4:58 PM
To: Peter Dalgaard
Cc: r-devel@stat.math.ethz.ch
Subject: Re: [Rd] Bug in new() or validObject() in methods package
(PR#7922)

murdoch@stats.uwo.ca writes:

Is it doing an extra eval or something?  It looks like it:

 > x <- expression()
 > x

expression()

 > eval(x)

NULL

 >
 > x <- quote(expression())
 > x

expression()

 > eval(x)

expression()

 > eval(eval(x))

NULL

You do realize that the two expression() results are not identical:

x <- quote(expression())
class(x)

[1] "call"

x <- expression()
class(x)

[1] "expression"

Not that I can fathom what bearing that has on the real problem...

I figured they weren't identical, given that they gave different results

  when eval'd, but I didn't know what the difference was exactly.
Thanks!

Duncan

______________________________________________
R-devel@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel