overwriting '<-' and infinite recursions
I wonder if you might be able to make use of R's "active bindings."
These enable you to set things up so that a user definable function is
called when an assignment is made or when a value is accessed. It's
sort of like overriding assignment for a particular variable, but you
don't need to mess with the definition of assignment.
Do
> apropos("binding")
to see the related functions. The help page for makeActiveBinding has a
simple example.
-- Tony Plte
Yi Zhang wrote:
Thanks, Luke. I would certainly be very happy to see any non-intrusive solution. The problem I'm dealing with is: I'm creating a new class which references some external resource (file or database) and I want to make the reference counting work. An example (-> means references): Initially we have symbol a -> object oa of my class -> file fa. Suppose then R code "b<-a" is executed. With no modification to the '<-' function, R would make another symbol b and bind it to oa. Imagine next "b[1]<-0" is executed. Here comes the trouble: R only knows to duplicate oa to another ob; the modification will be done to the underlying shared file fa. Of course, I have necessary code for overriding "[<-" and make that modification. The whole thing is because I'm not aware of any sharing of the external resource at the R level. That's the motivation for me to overwrite '<-' in the first place. Any potential alternative solutions? On Fri, Jan 23, 2009 at 4:25 PM, <luke at stat.uiowa.edu> wrote:
While it _may_ be possible to make this work in current R (I don't
know if it is) this is a Really Bad Idea as it will affect every other
piece of R code run on the system. It also may not work at all in
future versions of R (assignment is sufficiently core functionality
that it may not be implemented via a function at all in some
circumstances). Locked bindings are locked for a reason: we as
developers can assume that their values are what we intend them to be.
If those values are changed then that assumption fails and some things
may stop working.
If you explain what your needs are someone on the list can probably
help you find a more effective and less intrusive way of doing it.
luke
On Fri, 23 Jan 2009, Yi Zhang wrote:
Hello all,
I'm having a problem when overwriting the '<-' function and was told
I'd better post it here for help. The reason why I need to overwrite
it is complicated and not easy to tell in a few words; but this seems
the only clean option other than hacking R's core source code. My code
looks like:
# in .onLoad of a package; or if you want to test, put it in a function
env <- as.environment('package:base')
unlockBinding('<-',env)
assign('<-', newAssign, envir=env)
.Internal(lockBinding(as.name('<-'), env))
#not using lockBinding directly because it calls '<-'
It gave me this error: Error: evaluation nested too deeply: infinite
recursion / options(expressions=)?
Any suggestion is appreciated!
--
Yi
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-- Luke Tierney Chair, Statistics and Actuarial Science Ralph E. Wareham Professor of Mathematical Sciences University of Iowa Phone: 319-335-3386 Department of Statistics and Fax: 319-335-3017 Actuarial Science 241 Schaeffer Hall email: luke at stat.uiowa.edu Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu