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tracing something in a namespace (PR#7091)

2 messages · Richard M. Heiberger, John Chambers

Original
Richard M. Heiberger
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[1] "print.trellis"
Warning message: 
Assigning over the binding of symbol "print.trellis" in environment/package "lattice" 
in: .assignOverBinding(what, newFun, whereF)
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.

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

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


--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
1 day later
John Chambers
#
rmh@temple.edu wrote:
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.
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>
True, more or less.  We'll likely fix that for the next release, but the
recommended technique is as above for S3 methods.