>>>>> peter dalgaard <pda...@gmail.com>
>>>>> on Wed, 27 Aug 2014 21:09:47 +0200 writes:
> On 27 Aug 2014, at 16:48 , Hadley Wickham <h.wick...@gmail.com> wrote:
>>> I think the right answer _is_ to export the lazy data; the question is
how to do it. There's nothing particularly strange about exporting
non-functions ("letters" would be an example, save for the special status of
package:base). If you attach the package, the lazyloaded data appear in the
same environment as the exported function so they are de facto already in the
namespace for the purposes of library() and `::`. So I agree, something like
exportData() would be useful. (Or some other mechanism. You might want to be
able to export data selectively.)
>>
>> I don't think lazyloaded data are in the same environment as exported
>> functions - getExportedValue() (called by ::) looks first in the
>> "exports" namespace, then in the "lazydata" namespace:
>>
>> function (ns, name)
>> {
>> getInternalExportName <- function(name, ns) {
>> exports <- getNamespaceInfo(ns, "exports")
>> if (exists(name, envir = exports, inherits = FALSE))
>> get(get(name, envir = exports, inherits = FALSE),
>> envir = ns)
>> else {
>> ld <- getNamespaceInfo(ns, "lazydata")
>> if (exists(name, envir = ld, inherits = FALSE))
>> get(name, envir = ld, inherits = FALSE)
>> else stop(gettextf("'%s' is not an exported object from
>> 'namespace:%s'",
>> name, getNamespaceName(ns)), call. = FALSE, domain = NA)
>> }
>> }
>> ns <- asNamespace(ns)
>> if (isBaseNamespace(ns))
>> get(name, envir = ns, inherits = FALSE)
>> else getInternalExportName(name, ns)
>> }
>>
>>
>> (But maybe you just meant the library() and :: behaves as is lazydata
>> and exports were the same thing)
>>
>> Hadley
>>
>> --
>> http://had.co.nz/
> I meant that
> a) :: gives results as if the data was in the namespace
> b) if you do
>> library(MASS)
>> ls("package:MASS")
> [1] "abbey" "accdeaths" "addterm"
> [4] "Aids2" "Animals" "anorexia"
> [7] "area" "as.fractions" "bacteria"
> [10] "bandwidth.nrd" "bcv" "beav1"
> ....
> data and functions get put together in the same environment (however,
this is not the namespace environment, see later).
> What puzzles me is why the distinction between lazydata and exports was
there to begin with.
> The implication of the current setup is clearly that pkg::foo() cannot
access package::dat by referring to `dat` whereas it can do so if invoked as
library(pkg); foo().
> We also have
>> get("accdeaths", environment(MASS::addterm))
> Error in get("accdeaths", environment(MASS::addterm)) :
> object 'accdeaths' not found
>> library(MASS)
>> get("accdeaths", environment(MASS::addterm))
> Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov
> 1973 9007 8106 8928 9137 10017 10826 11317 10744 9713 9938 9161
> 1974 7750 6981 8038 8422 8714 9512 10120 9823 8743 9129 8710
> ...
> which confused me at first, but it actually just means that "accdeaths"
is found on the search path in the latter case. This strikes me as somewhat
dangerous: If a package uses one of its own datasets, it can be masked by a
later attach() or the global env.
> (I suspect that someone already explained all this a while back, but I
just wasn't listening at the time...)
I did say (as first reply in this thread) that the lazyloaded
datasets where in the package environment, but not
in the package's *namespace* environment -- which is somewhat
exceptional, as otherwise, the namespace envir is typically a superset
of the package envir, and I did mention the solution with
sysdata.rda + NAMESPACE which Brian and Hadley later mentioned, too.
However Michael did not get it well enough (because you
need to read other material), and I do think that is not an
ideal solution for data sets that have help pages, etc; notably
because creating sysdata.rda is not at all part of the package
sources, and hence harder for maintenance and "open source transparency".
The one additional important in the thread was the special
semantic of '::' which here returns something for
<pkg>::<obj> which is *not* part of the <pkg>'s namespace,
whereas the use of '::' does suggest to Joe Average to be
working with namespace (as opposed to package) contents.
I agree with your suggestion, Peter, that this looks more
confusing than it should, and ideally, we'd find a better setup.
OTOH, if we additionally allowed something like exportData(),
we would additionally get data that is both in the package and
namespace environments and other (not exported) data that is
only in the package, so add room for even more confusion.
Martin
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