On Sun, 18 Mar 2018, Jialin Ma wrote:
Dear all,
I am confused about the inconsistent behaviors of `@<-` operator when
used in different ways. Consider the following example:
library(inline)
# Function to generate an externalptr object with random address
new_extptr <- cfunction(c(), '
SEXP val = PROTECT(ScalarLogical(1));
SEXP out = PROTECT(R_MakeExternalPtr(&val, R_NilValue, val));
UNPROTECT(2);
return(out);
')
setClass("S4ClassHoldingExtptr", contains = "externalptr")
subs_extptr_1 <- function(x) {
x@.xData <- new_extptr()
x
}
subs_extptr_2 <- function(x) {
x <- `@<-`(x, ".xData", new_extptr())
x
}
I expect functions "subs_extptr_1" and "subs_extptr_2" should be
semantically identical. (is it right?)
No. The are similar but not identical. It is not a good idea to call
replacement functions directly and should be avoided. Doing so may need
to become a runtime error or at least a warning in the future.
Nevertheless, this is a bug in the implementation @<-.A simpler example is
x <- setClass("foo", slots = "bar")
x <- new("foo", bar = 1)
y <- x
y@bar
## [1] 1
`@<-`(x, bar, 2)
y@bar
## [1] 2
Will be fixed soon in R-devel.
Best,
luke
x <- setClass("foo", slots = "bar")
x <- new("foo", bar = 1)
y <- x
`@<-`(x, bar, 2)
An object of class "foo"
Slot "bar":
[1] 2
x
An object of class "foo"
Slot "bar":
[1] 2
x$bar
Error in x$bar : $ operator not defined for this S4 class
x@bar
[1] 2
But it seems that "subs_extptr_2" will modify its argument while
"subs_extptr_1" won't.
x <- new("S4ClassHoldingExtptr", new_extptr())
y <- x
y
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60971eb0>
subs_extptr_1(x)
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60974250>
x
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60971eb0>
y
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60971eb0>
As shown above, "subs_extptr_1" will not modify x or y.
subs_extptr_2(x)
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60973f30>
x
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60973f30>
y
# An object of class "S4ClassHoldingExtptr"
# <pointer: 0x7ffc60973f30>
However, "subs_extptr_2" will modify both x and y.
Is this behavior expected?
Thanks,
Jialin
sessionInfo()
R version 3.4.1 (2017-06-30)
Platform: x86_64-suse-linux-gnu (64-bit)
Running under: openSUSE Tumbleweed
Matrix products: default
BLAS: /usr/lib64/R/lib/libRblas.so
LAPACK: /usr/lib64/R/lib/libRlapack.so
locale:
[1] LC_CTYPE=en_US.UTF-
8 LC_NUMERIC=C LC_TIME=en_US.UTF-8
[4] LC_COLLATE=en_US.UTF-8 LC_MONETARY=en_US.UTF-
8 LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=en_US.UTF-
8 LC_NAME=C LC_ADDRESS=C
[10] LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8
LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices
utils datasets methods base
other attached packages:
[1] inline_0.3.14 magrittr_1.5
loaded via a namespace (and not attached):
[1] compiler_3.4.1 tools_3.4.1 yaml_2.1.18 ulimit_0.0-3
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--
Luke Tierney
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-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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