[R] package environment versus namespace environment

[Duncan Murdoch]

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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