On Fri, 23 Jan 2009, 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?
I'm still fuzzy about what you are trying to accomplish. You have
some code, say openFA(), that produces the oa value with
a <- openOA()
Then you could do
b <- a
and then
b[1] <- 0
or
a[1] <- 0
Do you want these to have the same effect, do you want a[1] <- 0 to do
one thing if b <- a has happened and another if not, should one signal
an error, ...?
From what you have written so far it would seem that messing with <-
would't really help as
d <- list(a)
and
f <- fuction(b) { ... }
f(a)
would create similar issues that would not be addressed.
luke
On Fri, Jan 23, 2009 at 4:25 PM, <l...@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: l...@stat.uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
--
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: l...@stat.uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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