[Rcpp-devel] Internals: how does DataFrame get initialized?

[Davor Cubranic]

On 2012-02-29, at 5:00 PM, Darren Cook wrote:

> Thanks for the reply Davor. It was a design question: why does
> DottedPair [2] have its own class? It does not add any member variables
> and it does not override any functions in its base class [1], so I
> assume it exists solely for code clarity [3]. I wondered what concept is
> was clarifying or representing.

I should let Romain and Dirk speak about their design choices here, but I think it will make more sense if you consider that both classes have a close relationship with R's SEXP union. So the pairlist "class" (i.e., the member of the C union) that is proxied by the DottedPair adds its own member variables (the CAR and CDR of the pair), and from the point of view of the consumer of the Rcpp API (you), it's as if those were internal to the DottedPair class, and not shared with any other subtype of the Robject hierarchy.

> [3]: Another way of saying that is that it seems I could move all
> DottedPair's functions into Robject, then write:
> 
>  class DottedPair: public Robject {}
> 
> and everything should still compile and work. (Or I've misunderstood
> something :-)

So this would have all of DottedPair's methods in Robject? What happens when you assign a non-pairlist SEXP (say, a vector) to an instance of Robject and then invoke one of the DottedPair's methods on it?

Davor