On Fri, 6 Oct 2006, Duncan Murdoch wrote:
> 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.
It might be a good idea to rethink the decision to have data be
handled specially instead of having data sets be treated as ordinary
exported variables. There may be a good reason for doing what we do
now but I don't know what it is. If there really is a good reason to
continue this then maybe we should think about this addition. It
doesn't feel like the right thing to do but may be harmless.
> 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.
No. :: exists precisely to allow code to access exported variables
without attaching the namespace. It is the only way I use this feature
and the reason the feature exists.
Best,
luke
>
> 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)
>> })
>> }
>>
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>
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--
Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: [EMAIL PROTECTED]
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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