conflict between rJava and data.table

On 01.03.2013 16:13, Simon Urbanek wrote:

On Mar 1, 2013, at 8:03 AM, Matthew Dowle wrote:

Simon Urbanek wrote :

Can you elaborate on the details as of where this will be a problem? Packages
should not be affected since they should be importing the namespaces from the
packages they use, so the only problem would be in a package that uses both
data.table and rJava --  and this is easily resolved in the namespace of such
package. So there is no technical reason why you can't have multiple
definitions of J - that's what namespaces are for.

Right. It's users using J() in their own code, iiuc. rJava's manual says "J is
the high-level access to Java."  When they use J() on its own they probably
want the rJava one, but if data.table is higher they get that one.
They don't want to have to write out rJava::J(...).

It is not just rJava but package XLConnect, too. If there's a better way would
be interested but I didn't mind removing J from data.table.

For packages there is really no issue - if something breaks in
XTConnect then the authors are probably importing the wrong function
in their namespace (I still didn't see a reproducible example,
though). The only difference is for interactive use so not having
conflicting J() [if possible] would be actually useful there, since
J() in rJava is primarily intended for interactive use.

Yes that's what I wrote above isn't it? i.e.

It's users using J() in their own code, iiuc.
"J is the high-level access to Java."

Not just interactive use (i.e. at the R prompt) but inside their functions and scripts, too.
Although, I don't know the rJava package at all. So why J() might be used for interactive
use but not in functions and scripts isn't clear to me.
Any use of J from example(J) will serve as a reproducible example; e.g.,

   library(rJava)          # load rJava first
   library(data.table)     # then data.table
   J("java.lang.Double")

There is no error or warning, but the user would be returned a 1 row 1 column
data.table rather than something related to Java. Then the errors/warnings follow from there.

The user can either load the packages the other way around, or, use ::

   library(rJava)                  # load rJava first
   library(data.table)             # then data.table
   rJava::J("java.lang.Double")    # ok now

Cheers,
Simon

Bunny/Matt,

To add to Steve's reply here's some background. This is well documented in NEWS
and Googling "data.table J rJava" and similar returns useful links to NEWS and
datatable-help (so you shouldn't have needed to post to r-devel).

From 1.8.2 (Jul 2012) :

o  The J() alias is now deprecated outside DT[...], but will still work inside
 DT[...], as in DT[J(...)].
 J() is conflicting with function J() in package XLConnect (#1747)
 and rJava (#2045). For data.table to change is easier, with some efficiency
 advantages too. The next version of data.table will issue a warning from J()
 when used outside DT[...]. The version after will remove it. Only then will
 the conflict with rJava and XLConnect be resolved.
 Please use data.table() directly instead of J(), outside DT[...].

From 1.8.4 (Nov 2012) :

o  J() now issues a warning (when used *outside* DT[...]) that using it
 outside DT[...] is deprecated. See item below in v1.8.2.
 Use data.table() directly instead of J(), outside DT[...]. Or, define
 an alias yourself. J() will continue to work *inside* DT[...] as documented.

From 1.8.7 (soon to be on CRAN) :

o  The J() alias is now removed *outside* DT[...], but will still work inside DT[...];
 i.e., DT[J(...)] is fine. As warned in v1.8.2 (see below in this file) and deprecated
 with warning() in v1.8.6. This resolves the conflict with function J() in package
 XLConnect (#1747) and rJava (#2045).
 Please use data.table() directly instead of J(), outside DT[...].

Matthew