[Rcpp-devel] Rcpp and ExternalPtr

[Tim Keitt]

On Mon, Dec 8, 2014 at 10:34 AM, Dirk Eddelbuettel <edd at debian.org> wrote:

>
> On 8 December 2014 at 09:58, Tim Keitt wrote:
> |
> |
> | On Sun, Dec 7, 2014 at 4:52 AM, Dirk Eddelbuettel <edd at debian.org>
> wrote:
> |
> |
> |
> |     What you are after, if I understand it correctly, is (close to) a
> common
> |     and
> |     well studied idiom called 'RAII': Resource Acquisition is
> Initialization.
> |     Two
> |     quick links, and you will find many more:
> |
> |
> |
> | I don't know if this example is helpful. Any class that can be
> initialized with
> | an SEXP and has an SEXP member function can be used as the argument or
> return
> | type from an Rcpp function call. I wrote this wrapper to avoid
> dereferencing
> | passed null pointers and as a return type for a lot of functions where I
> want
> | an R NULL return if the pointer is null.
>
> Nice post for the r-devel list :)  But as you don't use Rcpp here...
>

Touche...


>
> In essence Rcpp::XPtr does this for you.  If you rewrote the code in terms
> of
> Rcpp::XPtr, it might make for a nice post for the Rcpp Gallery.
>

When I eventually get back to R coding, I'll have to take another look at
XPtr. I do not recall now why I did not use it. Perhaps I wanted a single
point for checking null pointers transparently.

THK


>
> Dirk
>
> | THK
> |
> |
> | class
> | RGDALHandleWrapper
> |                         {
> |                         public:
> |                         RGDALHandleWrapper(void* h)
> |                         : handle(h) {} // If initialized NULL will
> return NULL
> |                         SEXP
> |                         RGDALHandleWrapper(const SEXP h)
> |                         : handle(R_ExternalPtrAddr(h))
> |                         {
> |                         if ( !handle ) stop("Null pointer passed to
> function\n"
> |                         );
> |                         }
> |                         operator SEXP() const
> |                         {
> |                         return handle ? // Return NULL SEXP on NULL
> pointer
> |                         R_MakeExternalPtr(handle, R_NilValue,
> R_NilValue) :
> |                         R_NilValue;
> |                         }
> |                         void* operator*() const { return handle; }
> |                         private:
> |                         void* handle;
> |                         };
> |
> |
> |
> |
> | --
> | http://www.keittlab.org/
>
> --
> http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org
>



-- 
http://www.keittlab.org/
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