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

[Duncan Murdoch]

On 4/2/2009 9:49 AM, Roger Peng wrote:
> 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.

Oops, I forgot about that.  So use a NAMESPACE plus an environment.

Duncan Murdoch

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