Cannot make std::vector<int8_t> from NumericVector about rcpp

[oleksii-nikolaienko]

Yes, thanks again

[eddelbuettel]

It's been a while but I have a faint recollection that this may be due char and int8_t clashing 'as they are both the same' and we weren't explicit about about preferring int8_t (which of course does not exist in R). And I guess we need to do what we do for char to that character variables work.

You can always write yourself a custom converter helper for this where the autoMAGIC dispatch fromt the compiler does not work. What you get from R will always be a int32_t so for example in one package where Rcpp is used this happens (and vec is the incoming variable from R

  } else if (dtype == "INT8") {
    IntegerVector v(vec);
    auto n = v.length();
    std::vector<int8_t> x(n);
    for (auto i=0; i<n; i++) {
      x[i] = static_cast<int8_t>(v[i]);
    }

I don't think there is much else you can do. If it bugs you greatly that the compiler complains, see if you can improve it without side effects to char and others. We would be interested ... but as int8_t is somewhat rare in R application this was never a priority.

(Going via interfaces that do know int8_t such as arrow might be an alternative too.)

[oleksii-nikolaienko]

Thanks for the explanation. I don't think I can improve as, that's beyond my expertise. So, I guess, I'll resort to static_cast as in your example.

FYI, I need this to write array tags to BAM files given the data from R, and these arrays can be of different type

[eddelbuettel]

Yep, I know. My day job is at TileDB and the lines I quoted were from our R package which may of course encounter different int sizes and signedness. Ditto with the single cell projects, VCF etc.

I think a one-off helper is fair workaround. Especially as template metaprogramming is hairy.

Ok to close this?