what is the preferred method to create a package local variable?

The use of an environment gets around the fact that package namespaces
are locked, so that values can't be changed once the package is
loaded. However, elements of environments can be changed.

-roger

On Thu, Apr 2, 2009 at 9:41 AM, Whit Armstrong <armstrong.whit at gmail.com> wrote:

Thanks to everyone for the suggestions.

The package local environment (per Roger Peng) works well.
.localstuff <- new.env()
.localstuff$bbg.db.conn <- dbConnect(...)

However, there is one thing that I'm confused about.

Why must the .localstuff variable be an environment?

I've tried the following, but the variable conn stays null during the
whole R session.  Despite the database connection succeeding (I can
see the constructor printing to the console):

conn <- NULL

.onAttach <- function(libname, pkgname) {
   conn <- dbConnect(dbDriver("PostgreSQL"), user="...")
}

.onUnload <- function(libpath) {
   dbDisconnect(conn)
}

output from R session:

[warmstrong at linuxsvr R.packages]$ R

library(KLS)

Loading required package: fts
Loading required package: RCommodity
Loading required package: unifiedDBI
Loading required package: RFincad
Loading required package: RLIM
Loading required package: RBoostDateTime
PostgresConnection::PostgresConnection()

KLS:::conn

NULL

x <- get.bbg("EURUSD Curncy")

Error in get.bbg("EURUSD Curncy") : Database connection not initialized

q()

PostgresConnection::~PostgresConnection()
[warmstrong at linuxsvr R.packages]$


Thanks,
Whit






On Tue, Mar 31, 2009 at 3:51 PM, Philippe Grosjean
<phgrosjean at sciviews.org> wrote:

The best way is to have those variable hidden in the package's workspace, as
explained by Roger Peng.

However, if you like to use a mechanism managing an environment specifically
dedicated to temporary variables very easily, look at assignTemp() and
getTemp() from svMisc package. The advantage is an easier sharing of such
variables between different packages (plus the bonus of easy management of
default values, overwriting or not of current content if the variable
already exists, ...). The temporary environment (TempEnv) is always located
in the forelast position just before 'base'.

In any cases, avoid using .GlobalEnv and the ugly <<- for that purpose.
Best,

Philippe Grosjean


Roger Peng wrote:

I usually use environments for this. So, in one of the R files for the
package, just do

.localstuff <- new.env()

Then, in functions you can do things like

.localstuff$bbg.db.conn <- dbConnect(...)

-roger

On Tue, Mar 31, 2009 at 11:45 AM, Whit Armstrong
<armstrong.whit at gmail.com> wrote:

for the moment, I'm using:

.onAttach <- function(libname, pkgname) {
  .bbg.db.conn <<- dbConnect(dbDriver("PostgreSQL"), user="blah","blah")
}

.onUnload <- function(libpath) {
  dbDisconnect(.bbg.db.conn)
}


which results in a hidden global variable in the global environment.

I would prefer to make the assignment only in the package namespace.
I've looked at assignInNamespace, but I can't seem to make it work.

Is there a preferred method for doing this?

When I try adding an assignment directly in the source file, I get the
"cannot change value of locked binding" error.

What am I missing?

Thanks,
Whit