From armstrong.whit at gmail.com  Thu Apr  2 15:41:00 2009
From: armstrong.whit at gmail.com (Whit Armstrong)
Date: Thu, 2 Apr 2009 09:41:00 -0400
Subject: [Rd] what is the preferred method to create a package local
	variable?
In-Reply-To: <49D27438.6010806@sciviews.org>
References: <8ec76080903310845x3b0a0c2cy22d30cd0799a206e@mail.gmail.com>
	<66f3bd910903311235w5421c11ap357ced8a6706f985@mail.gmail.com>
	<49D27438.6010806@sciviews.org>
Message-ID: <8ec76080904020641m7058120ckef7dd447a83a644@mail.gmail.com>

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
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>>
>>
>>
>



[Rd] what is the preferred method to create a package local variable?
Whit Armstrong