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...)
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd....@cbs.dk Priv: pda...@gmail.com
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