On 07/03/2014 10:16 AM, Benjamin Tyner wrote:
Hello,
I realize that a function in <environment: base> (for example, function
"head1" below) is unable to see (without resorting to "::", anyway)
objects in utils (for example, "head" below), since package:base is
after package:utils on the search path.
However, I'm wondering what is the machinery that allows a function in
<environment: namespace:base> (for example, function "head2" below) to
be able to see "head" just fine, without needing to resort to "::".
See Luke Tierney's article in R News,
Name space management for R. Luke Tierney, R News, 3(1):2-6, June 2003
<http://cran.r-project.org/doc/Rnews/Rnews_2003-1.pdf>
There's a link to it from the R help system. Run help.start(), then
look at "Technical papers" in the Miscellaneous Material section.
I believe most of what it says is still current; the only thing I can
see at a glance that is no longer correct is that in those days
namespaces were optional in packages. Now all packages have namespaces.
Duncan Murdoch
I'm also wondering more generally, why there is a need (practically
speaking) for a distinction between the environment associated with a
package and the environment associated with the namespace.
$ export R_PROFILE=/home/btyner/Rprofile.site
$ cat /home/btyner/Rprofile.site
sys.source("/home/btyner/head1.R", envir = baseenv())
sys.source("/home/btyner/head2.R", envir = .BaseNamespaceEnv)
$ cat /home/btyner/head1.R
head1 <- function(x) head(x)
$ cat /home/btyner/head2.R
head2 <- function(x) head(x)
$ Rscript -e "head1(letters)"
Error in head1(letters) : could not find function "head"
Execution halted
$ Rscript -e "head2(letters)"
[1] "a" "b" "c" "d" "e" "f"
$ Rscript -e "sessionInfo()"
R version 3.0.1 (2013-05-16)
Platform: x86_64-pc-linux-gnu (64-bit)
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
[3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=en_US.UTF-8 LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=C LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets base
Regards
Ben
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