On 14-03-08 6:42 PM, Benjamin Tyner wrote:
Duncan,
Thank you for the informative link. So, do the loaded namespaces have an
"ordering" akin to the package search path that determines that
functions in the base namespace can see objects in the utils namespace?
(I noticed that loadedNamespaces() just comes back in alphabetical order.)
No. The article that Henrik cited gives a reasonable description up
until near the end, where (in my opinion) it makes things unnecessarily
complicated. I'd recommend that you stop reading around where he tries
to explain the dotted lines. In particular, ignore the second version
of the "Map of the World"; the first one is accurate, the second is just
misleading.
In answer to your question: Gupta's article misses the possibility of
packages that are loaded but not in the search path. In the notation of
the first part of that article, loading a namespace just puts it in the
middle two columns (i.e. creates the namespace and imports environments)
without putting it in the search list. That happens when you import or
load a package without attaching it. The search path imposes an
ordering, things that aren't in it aren't ordered.
Duncan Murdoch
Regards
Ben
On 03/07/2014 11:46 AM, Duncan Murdoch wrote:
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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