Romain's solution is almost certainly the way to go.
Just for completeness, note that you can define a field on the R side to
be an accessor function as well, using the standard mechanism for active
bindings; i.e., an R function (anonymous if you want) that returns the
field if called without argument and sets it (or gives an error) with
an argument.
John
On 11/18/10 1:47 PM, Douglas Bates wrote:
Thanks again Romain. Now that you mention it I remember.
On Thu, Nov 18, 2010 at 3:41 PM, Romain Francois
<[email protected]> wrote:
Le 18/11/10 22:31, Douglas Bates a écrit :
My C++ coding style (such as it is) has been influenced by reading
Frank Bokken's "C++ Annotations". I keep most data members of classes
private or protected and usually with names like d_x, d_y, d_weights,
etc. then provide accessor functions named x, y, weights, etc.
Generally the accessors return const references.
If I export such a class in an Rcpp module I can't allow field access
but can allow access from R to the accessor methods. This seems
slightly awkward in that the user must know to use
myRefObj$x()
instead of
myRefObj$x
to access the x field. Any strong opinions about fields access versus
access to field accessor methods?
As an example, one of my classes ends up looking like this
getRefClass("Rcpp_lmResp")
Generator object for class "Rcpp_lmResp":
No fields defined
Class Methods:
"callSuper", "export", "finalize", "import", "initFields",
"initialize", "mu",
"offset", "sqrtrwt", "sqrtXwt", "updateMu", "updateWts", "wrss", "wtres",
"y"
Reference Superclasses:
"envRefClass"
but all those methods except updateMu and updateWts are field accessors.
One advantage of this method is that one can't make changes to those
fields at the R level, which I like because I am paranoid about
introducing inconsistencies in the fields.
You can use .property instead of .field to short circuit x back to d_x.
Consider this class (which I believe follows the convention you mention):
class Simple {
public:
Simple( double x ) : d_x(x){} ;
const double& x(){ return d_x ;}
private:
double d_x ;
} ;
In R, you'd want to be able to do :
r<- new( Simple, 10 )
r$x
but not :
r$x<- 20
Then .property is what you need:
RCPP_MODULE(mod){
class_<Simple>( "Simple" )
.constructor(init_1<double>())
.property( "x" ,&Simple::x )
;
}
When the third argument is not given, the property is considered read only.
Romain
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