[Rd] Coercing from a local class to a foreign one

[Sean Davis]

I am working on writing a fairly simple package that defines several
classes.  However, there are several other packages that deal with the same
types of data, so I would like to methods for coercing my classes to those
of the other packages.  Easy enough.  However, I would really like to just
"suggest" those other packages, as my own doesn't rely on them at all.  If I
do so and the other packages are not available and loaded, I get warnings on
loading my own package that the classes from the foreign packages are not
available.  I understand that these messages are not significant, but is
there a way to suppress them on loading.  As far as I can tell, this is
specific to S4 coercion methods where the classes to coerce to or from may
not be loaded or defined at the time of loading a package.

Any hints?  (In other words, what did I miss in the documentation....)

Thanks,
Sean