[Rd] switch to reference counting in R-devel

[Tierney, Luke]

Baring any unforeseen issues R-devel will switch in about a week from
the NAMED mechanism to reference counting for determining when objects
can be safely mutated in base C code. This is expected to have minimal
impact on packages not using unsupported coding practices in their C
code.


The transition to reference counting has been in progress for a
number of years. Some older notes on this are available at
http://developer.r-project.org/Refcnt.html.  These may no longer be
completely accurate but should give you an idea of what is going on.

If you want to test your package under reference counting you can do
so by building R with -DSWITCH_TO_REFCNT added to CFLAGS or DEFS in a
config.site file.

A small number of packages are still using the NAMED or SET_NAMED
functions even though this has been discouraged for some  time.
For now these will not produce errors but also not do anything useful.
They will probably be removed before R 4.0.0 is released, so you
should look at why you are using them and adjust accordingly.

Best,

luke


-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney using uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu