Hi Whit --
Whit Armstrong <armstrong.w...@gmail.com> writes:
> 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?
I don't konw about preferred, but one method is
pkgVars <- local({
x <- NULL
list(getX=function() x, setX=function(value) x <<- value)
})
with use
> pkgVars$getX()
NULL
> pkgVars$setX(123)
> pkgVars$getX()
[1] 123
This introduces a different programming paradigm (a list of functions)
that might not be familiar for end-users and is not readily amenable
to documentation. A probably better way is
pkgVars <- new.env(parent=emptyenv())
getX <- function() get("x", pkgVars, inherits=FALSE)
setX <- function(value) assign("x", value, envir=pkgVars)
> getX()
Error in get("x", pkgVars, inherits = FALSE) : object 'x' not found
> setX(123)
> getX()
[1] 123
A tidier response to the first getX() could be arranged with something
like
pkgVars <- local({
env <- new.env(parent=emptyenv())
env[["x"]] <- NULL
env
})
pkgVars, getX, and setX can be exported from the name space or not.
FWIW, usually one wants .onLoad rather than .onAttach, so that a
package import-ing your package (not just depend-ing, or when used
directly in an interactive session) will execute the setup code.
Hope that helps and is not too misleading.
Martin
> 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
>
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> https://stat.ethz.ch/mailman/listinfo/r-devel
--
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109
Location: Arnold Building M2 B169
Phone: (206) 667-2793
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