[Rcpp-devel] feature proposal: ListOf

[romain at r-enthusiasts.com]

Le 2013-10-26 22:57, Kevin Ushey a écrit :
> Other thing worth considering for implementation: how might it fit in
> with Rcpp Attributes? It would be very nice if we could define a
> function like
>
> // [[Rcpp::export]]
> ListOf<IntegerVector> fun( ListOf<IntegerVector> x ) {
>    ...
> }
>
> and have the wrapper function automatically generated as we're used
> to. Ideally, ListOf would have most of the non-ctor methods from List
> as well.

Could make ListOf derive from List instead of having it contain a List

> Should the constructor do validation on the contents (ensure all
> elements in the ListOf object have the template type)? Or could that
> be part of a separate method (e.g. validate)?

I'd put this in the same bucket as bounds check. Something kind of nice 
conceptually, but too expensive.

For example in dplyr, I'm using ListOf where I already exactly know the 
type.

> That said, this would be a lot of work and I understand if it's not a
> priority. I'd like to contribute to the implementation but my C++
> programming chops aren't up to par yet... unit tests and examples, I
> can gladly contribute though.

You can always try :)

> Let me know if you get a chance to revisit this later.

I will.

> -Kevin
>
> On Fri, Oct 25, 2013 at 12:00 PM, Romain Francois
> <romain at r-enthusiasts.com> wrote:
>> Cool. I've got lots on my plate right now, so this is not a 
>> priority.
>> Did you have a chance to look at the (simplistic) implementation of 
>> ListOf
>> in dplyr:
>> 
>> https://github.com/hadley/dplyr/blob/master/inst/include/tools/ListOf.h
>>
>> The indexing operator should be proxified so that we could handle
>> assignments, i.e.:
>>
>> NumericVector z ;
>> ListOf<NumericVector> x( xxx );
>> x[0] = z ;
>>
>> At the moment it only has read access because that's all I needed 
>> for now in
>> dplyr.
>>
>> So maybe if we wanted something more generic in Rcpp, this should be
>> designed a bit more.
>>
>> Romain
>>
>> Le 25/10/2013 20:40, Kevin Ushey a écrit :
>>
>>> Hi Romain, Dirk,
>>>
>>> I'd be willing to contribute an Rcpp Gallery post and some tests if
>>> this were added to Rcpp; I think it would be quite useful.
>>>
>>> -Kevin
>>>
>>> On Wed, Oct 23, 2013 at 6:31 AM, Dirk Eddelbuettel <edd at debian.org> 
>>> wrote:
>>>>
>>>>
>>>> On 23 October 2013 at 14:31, Romain Francois wrote:
>>>> | Le 23/10/2013 13:47, Dirk Eddelbuettel a écrit :
>>>> | > As always, preferably with a usage example (Rcpp Gallery post?
>>>> Section in a (new)
>>>> | > vigntte?) and tests so that people have some info on how to 
>>>> use it.
>>>> |
>>>> | That means it will take me more time than what I wanted to 
>>>> commit to
>>>> | this. I'll come back to it later then.
>>>>
>>>> Up to you.  FWIW your previous commits are still undocumented in 
>>>> NEWS.Rd.
>>>>
>>>> Dirk
>>>>
>>>> --
>>>> Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
>>
>>
>>
>> --
>> Romain Francois
>> Professional R Enthusiast
>> +33(0) 6 28 91 30 30
>>