no visible binding for global variable for data sets in a package
On 27 Aug 2014, at 16:48 , Hadley Wickham <h.wickham at 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.mes at cbs.dk Priv: PDalgd at gmail.com