R devel - Nov 2005 - import of Namespaces

Dear R devels,

let's say I have three packages "pkg1", "pkg2" and
"pkg3" which all
contain new S4 classes and methods. Where "pkg3" depends on
"pkg2" and
"pkg2" depends on "pkg1". Moreover, all three packages have
namespaces.

1) I use ".onLoad <- function(lib, pkg) require(methods)". Do I
also
have to import the namespace of "methods" package?

2) If I use import("pkg1") in the namespace of "pkg2", does
this also
(correctly) import the S4 classes and methods of "pkg1"? Or do I 
explicitly have to use importClassesFrom resp. importMethodsFrom?

3) If I import the Namespace of "pkg2" in "pkg3", where the
namespace of
"pkg2" has import("pkg1") (or maybe importClassesFrom, 
importMethodsFrom) and I also want to use S4 classes and methods of 
"pkg1" in "pkg3". Is it sufficient to have
import("pkg2") in the
Namespace of "pkg3" or do I need import("pkg1") and
import("pkg2")?

Many thanks for your help and advice
Matthias

-- 
StaMatS - Statistik + Mathematik Service
Dipl.Math.(Univ.) Matthias Kohl
www.stamats.de

My understanding is of your questions is below:

Matthias Kohl wrote:
> Dear R devels,
> 
> let's say I have three packages "pkg1", "pkg2" and
"pkg3" which all
> contain new S4 classes and methods. Where "pkg3" depends on
"pkg2" and
> "pkg2" depends on "pkg1". Moreover, all three packages
have namespaces.
> 
> 1) I use ".onLoad <- function(lib, pkg) require(methods)". Do
I also
> have to import the namespace of "methods" package?
No.
> 
> 2) If I use import("pkg1") in the namespace of "pkg2",
does this also
> (correctly) import the S4 classes and methods of "pkg1"? Or do I 
> explicitly have to use importClassesFrom resp. importMethodsFrom?
Importing an entire package namespace will import all of the exported 
classes/methods from "pkg1".
> 
> 3) If I import the Namespace of "pkg2" in "pkg3", where
the namespace of
> "pkg2" has import("pkg1") (or maybe importClassesFrom, 
> importMethodsFrom) and I also want to use S4 classes and methods of 
> "pkg1" in "pkg3". Is it sufficient to have
import("pkg2") in the
> Namespace of "pkg3" or do I need import("pkg1") and
import("pkg2")?
I believe you need to import each separately since the S4 
classes/methods from "pkg1" will not be available to you simple
because
you imported "pgk2" (i.e. I don't think the chain rule applies
here).
> 
> Many thanks for your help and advice
> Matthias
> 
-- 
Roger D. Peng  |  http://www.biostat.jhsph.edu/~rpeng/