external pointers

On Mon, 12 Dec 2005, Roger Bivand wrote:

Where would be best to read about externalptr? I'm having trouble
finding material in the manuals or the site-search.

And would I need to use all the .Call machinery and C headers and  
SEXP
etc in order to handle externalptr objects?

One package using externalptr is rgdal - Tim Keitt wrote the  
bindings to
the external GDAL library for reading raster images to first return a
pointer to a dataset (on disk) opened by GDAL, then to use the  
object to
retrieve (parts of) the data. Most of the .Call/SEXP machinery is  
there
(for the C++ case, GDAL is C++, so GDAL manages its own memory for  
its
objects). The package also uses S4 classes, which may be overkill  
for your
purposes.

RODBC is another, somewhat simpler, one.

There is documentation on developer.r-project.org, but my  
recollection is
that is was not up to date (and in particular not re finalizers).   
On my
TODO list is to add end-user documentation to `Writing R Extensions'.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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Oxford OX1 3TG, UK                Fax:  +44 1865 272595