[Rcpp-devel] syntactic sugar

[Romain Francois]

On 03/01/2010 01:48 PM, Dirk Eddelbuettel wrote:
>
> On 1 March 2010 at 12:20, Romain Francois wrote:
> | Hello,
> |
> | I'm starting to find the Named construct somewhat too verbose and I'd
> | like to add some syntactic sugar.
> |
> | I've commited something just now. I'd like to ear opinions about it.
> |
> | The machinery is built around the classes
> | Rcpp::internal::NamedPlaceHolder, Rcpp::internal::NamedPlaceholderProxy
> | and the Rcpp::_ object which is a static instance of NamedPlaceHolder.
> |
> | Here is an example :
> |
> | require( inline )
> | require( Rcpp )
> | funx<- cfunction(signature(), '
> | 	Language call( "rnorm", _["mean"] = 10 ) ;
> | 	return call ;
> | ', Rcpp = TRUE, includes = "using namespace Rcpp;"  )
> | funx()
> |
> |
> | The interesting thing is
> |
> |   _["mean"] = 10
> |
> | which is the same as Named( "mean", 10 )
>
> On purely stylistic grounds, I dislike it.
>
> | There is also the ARG macro in Rcpp.h
> |
> | #define ARG(name) ::Rcpp::internal::NamedPlaceholderProxy name(#name) ;
> |
> | which allows the syntax :
> |
> | funx<- cfunction(signature(), '
> | 	ARG(mean)
> | 	Language call( "rnorm", mean = 10 ) ;
> | 	return call ;
> | ', Rcpp = TRUE, includes = "using namespace Rcpp;"  )
> |
> |
> | There is the annoying bit of calling the macro, but I suppose an
> | application could have calls to ARG in some header.
> |
> | Any ideas ? Suggestions ...
>
> If you feel must give users this rope, the let's do it.
>
> I mostly try to follow the rule of 'no #defines in C++'. Ie no macros.
> Typedefs, sure.  The ARG one is useful so we could make it available but I
> would not use it.  There is, it seems based on a quick glance, a way to use
> this as
>
>        typedef ::Rcpp::internal::NamedPlaceholderProxy rcppProxy;
>
> and that would be good enough for me.
>
> But heck, there are only two of us voting here so if it is a tie and you
> really want it, go for it.
>
> Dirk

We can do :

Language call( "rnorm", Named("mean") = 10 ) ;

which I find slightly less annoying than ;

Language call( "rnorm", Named("mean", 10) ) ;

Maybe I can remove the _ but leave the classes so that the user can do :

NamedPlaceHolder args ;
Language call( "rnorm", args["mean"] = 10 ) ;

The ARG macro is for the lazy ones who do not want to type the name of 
the argument twice.

NamedPlaceholderProxy mean("mean") ;

but then maybe ARG is not enough encapsulated a name, maybe something 
like RCPP_REGISTER_ARGUMENT or something, dunno.

Anyone else out there with opinions ?

Romain

-- 
Romain Francois
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