[Rcpp-devel] Default value for Rcpp List

[Dirk Eddelbuettel]

On 14 August 2013 at 11:42, Matteo Fasiolo wrote:
| Dear Rcpp users,
| 
|  a very simple question: I have a function that has a Rcpp::List
| among its arguments, and I would like to set a default values for
| that List.
| Unfortunately this code:
| 
| cppFunction(
|   '
|   List myList(List x = List::create(_["a"] = 1, _["b"] = 2))
|  {
|   return x;
|  }
|  ' 
| )
| 
| raises the warning:
| 
| 
| Warning message:
| Unable to parse C++ default value 'List::create(_["a"] = 1, _["b"] = 2)' for argument x of function myList
| >
| > myList()
| Error in .Primitive(".Call")(<pointer: 0xb5907fb0>, x) : 'x' is missing
| 
| 
| Similar code with NumericVector works fine:
| 
| cppFunction(
|   '
|   NumericVector myVett(NumericVector x = NumericVector::create(3))
|  {
|   return x;
|  }
|  ' 
|  )
| 
| myVett()
| # [1] 0 0 0

Not really. You just allocated space, not values.

I suspect this doesn't work the way you want it to.
 
| Am I doing something wrong? Thanks!

You could create the objects "empty", test in the function body for emptyness
and set values.

Dirk
 
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-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com