Re: [Rd] tracing something in a namespace (PR#7091)

From: John Chambers <jmc_at_research.bell-labs.com>
Date: Fri 16 Jul 2004 - 07:43:21 EST

rmh@temple.edu wrote:
>
> # Your mailer is set to "none" (default on Windows),
> # hence we cannot send the bug report directly from R.
> # Please copy the bug report (after finishing it) to
> # your favorite email program and send it to
> #
> # r-bugs@r-project.org
> #
> ######################################################
>
> > x <- rnorm(10)
> > y <- 1:10
> > xyplot(y ~ x)
> > trace(lattice:::print.trellis, exit=recover)
> [1] "print.trellis"
> Warning message:
> Assigning over the binding of symbol "print.trellis" in environment/package "lattice"
> in: .assignOverBinding(what, newFun, whereF)
> > xyplot(y ~ x)
> > untrace(lattice:::print.trellis)
> Error in untrace(lattice:::print.trellis) :
> Argument what should be the name of a function
> >
>
> Something isn't right. I see three possibilities.
>
> a. tracing something in a namespace is prohibited and I didn't get an error,
> instead I got a warning.

No, it's not prohibited, though it's not encouraged.

Not to be counted on as being guaranteed to exist forever.

Use the alternative under b.

>
> b. tracing in a namespace is acceptable, but the trace didn't work.

I believe your problem has to do with S3 methods in namespaces. Effectively, the first dispatch of an S3 method in a namespace caches the method found (at least that is my impression).

If I take your example and move the trace() call before the first call to xyplot() (and therefore before the first dispatch of print.trellis) it works for me.

But, then you cannot redefine the method, so untrace() wouldn't work in any case.

DON'T USE trace() ON S3 METHODS IN NAMESPACES.

Instead, a mechanism that is slightly more cumbersome but perfectly legal (and no warnings) is to copy the S3 method to the global environment and trace it there.

As long as the method is being dispatched, not called directly inside the namespace, then the global copy will be used.

For your example:

R> print.trellis <- lattice:::print.trellis
R> trace(print.trellis, exit = recover)
R> x <- rnorm(10)
R> y <- 1:10
R> xyplot(y ~ x)

Tracing print.trellis(yy$value) on exit

Enter a frame number, or 0 to exit

1:source("~/testR/latticeTrace.R", echo = T) 
2:print(yy$value) 
3:print.trellis(yy$value) 

Selection: 0
R> untrace(print.trellis)
R> xyplot(y ~ x)
R> 

>
> c. untrace doesn't recognize lattice:::print.trellis as the name of a function,
> even though trace did.

True, more or less. We'll likely fix that for the next release, but the recommended technique is as above for S3 methods.

>
> --please do not edit the information below--
>
> Version:
> platform = i386-pc-mingw32
> arch = i386
> os = mingw32
> system = i386, mingw32
> status =
> major = 1
> minor = 9.1
> year = 2004
> month = 06
> day = 21
> language = R
>
> Windows XP Home Edition (build 2600) Service Pack 1.0
>
> Search Path:
> .GlobalEnv, file:c:/HOME/rmh/hh/splus.library/HH/.RData, package:methods, package:stats,
> package:utils, package:multcomp, package:mvtnorm, package:abind, package:graphics,
> package:lattice, package:grid, Autoloads, package:base
>
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-devel

-- 
John M. Chambers                  jmc@bell-labs.com
Bell Labs, Lucent Technologies    office: (908)582-2681
700 Mountain Avenue, Room 2C-282  fax:    (908)582-3340
Murray Hill, NJ  07974            web: http://www.cs.bell-labs.com/~jmc

______________________________________________
R-devel@stat.math.ethz.ch mailing list
https://www.stat.math.ethz.ch/mailman/listinfo/r-devel
Received on Fri Jul 16 07:48:00 2004

This archive was generated by hypermail 2.1.8 : Wed 03 Nov 2004 - 22:45:02 EST