[Rd] conflict between rJava and data.table

[Matthew Dowle]

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.

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