[Rd] external pointers

[Prof Brian Ripley]

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)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595