On 10/6/2006 9:05 AM, [EMAIL PROTECTED] wrote:
> Full_Name: Thomas Friedrichsmeier
> Version: 2.4.0
> OS: GNU/Linux
> Submission from: (NULL) (84.61.116.51)
>
>
> Since R 2.4.0, operator "::" also returns objects in the package environment,
> if
> the package does not have a namespace. This is a very welcome addition.
>
> Additional wish:
> If a package has a namespace, but does not place all symbols in that
> namespace,
> lookup will still fail. For example in package boot (version 1.2-26):
>
> library (boot)
> exists ("motor", envir=as.environment ("package:boot")) # TRUE
> getAnywhere ("motor") # found in
> package:boot
> boot::motor # error not in
> namespace
>
> This is as documented, but I think it would be convenient, if boot::motor
> would
> also return the object in this case.
At first I was ready to disagree with you, telling you to use the ":::"
operator for something that is not exported: but in fact motor is a
dataset, so it is exported from the package by being loaded into the
package environment when the package is loaded. I agree that the "::"
operator should find it.
I think the rule should be: the "::" operator looks at the symbols that
are publicly available from the package, i.e. boot::motor should
effectively be an abbreviation for
get("motor", pos="package:boot", inherits=FALSE)
after making sure boot is loaded. I think getExportedValue() is a much
more rarely needed function, so users should need to use it explicitly.
Duncan Murdoch
>
> This might be achieved by adding an additional tryCatch in "::": If the
> package
> has a namespace, try getExportedValue (), if that fails, try to get from
> package
> environment instead. E.g.:
>
> "::" <- function (pkg, name)
> {
> pkg <- as.character(substitute(pkg))
> name <- as.character(substitute(name))
> ns <- tryCatch(asNamespace(pkg), hasNoNamespaceError = function(e) NULL)
> if (is.null(ns)) {
> pos <- match(paste("package", pkg, sep = ":"), search(),
> 0)
> if (pos == 0)
> stop(gettextf(paste("package '%s' has no name space and",
> "is not on the search path"), pkg), domain = NA)
> get(name, pos = pos, inherits = FALSE)
> }
> else tryCatch(getExportedValue(pkg, name), error=function (e) {
> pos <- match(paste("package", pkg, sep=":"), search(),
> 0)
> get(name, pos, inherits=FALSE)
> })
> }
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
