[Rcpp-devel] ListOf -- update

Kevin Ushey kevinushey at gmail.com
Tue Oct 29 05:02:17 CET 2013

Hi guys,

With some encouragement from Romain, I took a shot at implementing the
ListOf<T> class. For now, everything's just in one big .cpp file here
(later I can factor it out to .h and .cpp files). But please take a
look here:


I took Romain's suggestions from before and 1) have ListOf<T>
inheriting from List directly, and 2) proxified operator[] so we can
distinguish read / write (merci, Scott Meyers, for More Effective
C++). Ultimately, most of it is boilerplate used so that the proxy is
handled correctly.

The class isn't too complicated, but it is surprisingly functional
since it can leverage everything already available in Rcpp. It works
well with the sugar functions and it can be handled by Rcpp attributes
as-is as well. There are a couple of demonstrative examples at the
bottom (to be written as a more formal test suite later).

I would welcome any comments; I'm fairly inexperienced as a C++
programmer so I'm sure some things might be wrong.

Things I know could be better and would appreciate some advice on:

1) Use Rcpp's traits system rather than TYPEOF for mapping template
types to strings (ie. in validate), (eg: going from Rcpp classes to
internal SEXP types; more generally, how can I navigate the traits

2) Extend lapply, sapply to infer types for applied templated
functions from ListOf<T> classes, so for e.g. a ListOf<NumericVector>
x and a template function add_1, we could just write

    lapply(x, add_1);

rather than

    lapply(x, add_1<NumericVector>);



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