Le 18/11/10 22:41, Romain Francois a écrit :
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
For convenience, here is the full example :
require( Rcpp )
require( inline )
inc <- '
class Simple {
public:
Simple( double x ) : d_x(x){} ;
const double& x(){ return d_x ;}
private:
double d_x ;
} ;
RCPP_MODULE(mod){
class_<Simple>( "Simple" )
.constructor(init_1<double>())
.property( "x" , &Simple::x )
;
}
'
fx <- cxxfunction( , '', includes = inc, plugin = "Rcpp" )
mod <- Module( "mod", getDynLib( fx ) )
Simple <- mod$Simple
r <- new( Simple, 10 )
r$x
r$x <- 20
--
Romain Francois
Professional R Enthusiast
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http://romainfrancois.blog.free.fr
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