[Rd] methods package: inheriting from structures; group generics

[John Chambers]

Now that 1.5 is released, some changes have been committed to the
r-devel version of the methods package.

They are mostly bug fixes (or making things work more as users would
expect) in two areas:

1.  new classes that extend one of the basic datatypes that have
attributes but had no class attribute in S3 (e.g., "matrix" or "ts"). 
The previous code didn't handle the attributes properly and the new()
function didn't work as it should.

2.  group generic functions when the members of the group were
primitives.  Because the members of the group are never actual generic
functions (for reasons of efficiency), there was no easy way to turn
method dispatch on, and the callGeneric function was unable to find the
generic definition.

It is still necessary to turn method dispatch on in this case (see
?setGeneric) by calling something like:

 setGroupGeneric("Arith")

This requirement may be dropped later, depending on experience.

-- 
John M. Chambers                  jmc@bell-labs.com
Bell Labs, Lucent Technologies    office: (908)582-2681
700 Mountain Avenue, Room 2C-282  fax:    (908)582-3340
Murray Hill, NJ  07974            web: http://www.cs.bell-labs.com/~jmc
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