On 22/06/2020 1:40 p.m., Bert Gunter wrote:
...
and just to add to the query, assume the author of pkg B did (does) not
know of pkg A and so, for example, could (did) not import any of pkg A's
content into B. Given that there are at the moment ~20,000 packages out
there, this does not seem to be an unreasonable assumption. One may even
further assume that the user may not know that (s)he has package B loaded,
as it may be a dependency of another package that (s)he uses. I certainly
don't keep track of all the dependencies of packages I use.
Under these assumptions, is there any more convenient alternative to
Wolfgang's pkgA:foo(x) explicit call under such assumptions? If pkgA has a
long name, what might one do?
It's always possible to make a new name, e.g.
fooA <- pkgA::foo
fooB <- pkgB::foo
If you are writing a package, this can be done in the NAMESPACE file, e.g.
importFrom(pkgA, fooA = foo)
though this doesn't appear to be documented in the usual places.
Duncan Murdoch
Bert Gunter
"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Mon, Jun 22, 2020 at 10:00 AM Viechtbauer, Wolfgang (SP) <
wolfgang.viechtba...@maastrichtuniversity.nl> wrote:
Hi All,
Let's say there are two packages pkgA and pkgB, both of which have a
generic function
foo <- function(x, ...)
UseMethod("foo")
and pkgA has a method for objects of class "A":
foo.A <- function(x, ...)
print(x)
and pkgB has a method for objects of class "B":
foo.B <- function(x, ...)
plot(x)
Both packages export foo and their method and declare their respective S3
methods, so:
export(foo)
export(foo.A)
S3method(foo, A)
in NAMESPACE of pkgA and
export(foo)
export(foo.B)
S3method(foo, B)
in NAMESPACE of pkgB.
If a user loads pkgA first and then pkgB, this fails:
library(pkgA)
library(pkgB)
x <- 1:4
class(x) <- "A"
foo(x)
Error in UseMethod("foo") :
no applicable method for 'foo' applied to an object of class "A"
and vice-versa. Of course, pkgA::foo(x) works. Aside from pkgA importing
foo() or vice-versa, is there some other clever way to make this work? In
earlier versions of R (at least in 3.6.3), this used to work (i.e., the
generic foo() from pkgB would find method foo.A() and vice-versa), but not
since 4.0.0.
Best,
Wolfgang
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