Le 17/04/2018 à 17:53, Dirk Eddelbuettel a écrit :
On 17 April 2018 at 10:31, Dirk Eddelbuettel wrote:
|
| On 17 April 2018 at 15:09, Serguei Sokol wrote:
...
| | It will automatically coerce NULL to a declared vector type.
| | It's a more primitive solution than Nullable<T> but in many cases
| | it can be largely sufficient and make code look shorter and clearer.
| |
| | Will it break something in established usage habits? Is it compatible with
your plans for Rcpp?
| | I can prepare a PR if you decide to include it.
|
| We could test that. It may not do harm -- so I just turned on a rev.dep
| check for it.
|
| Can you open an issue for it on GH though? Better visibility and easier 'per
| concrete topic' discussion.
I was just about to do so when I saw your post here. So let decide if
the semantic is useful or not and if yes, we'll switch to GH. OK?
I am not convinced that the semantics are useful. Your example works on the
arma type (where we our very old design issue of always returning a matrix):
What is returned: a matrix or a vector is not important here. By the way, it is
already resolved by an optional RCPP_ARMADILLO_RETURN_COLVEC_AS_VECTOR macro,
remember?
The point here is how the /input/ NULL is interpreted. Is it coerced to smth or
just an error is thrown?
sourceCpp("/tmp/serguei.cpp")
f(NULL)
[,1]
f(integer(0))
[,1]
f()
Error in f() : argument "x" is missing, with no default
Normal. If you want to make the parameter optional, you have to declare
vec f(Rcpp::NumericVector x=R_NilValue) {return x+1;}
> f()
[,1]
It does not work yet with 'vec' type but it could with an appropriate patch.
We are just discussing the usefulness of semantics not yet the patch.
class(f(NULL))
[1] "matrix"
(not a big deal what is returned as discussed above).
But if I do the same with Rcpp types, say a matrix via
// [[Rcpp::export]]
Rcpp::NumericMatrix g(Rcpp::NumericMatrix x) { return x+1; }
then I get more restrictive behaviour (as NumericMatrix tests for matrix)
Right. I think that the next logical step would be to allow an automatic
coercion of atomic vectors to matrices too. As in R
> as.matrix(integer(0))
[,1]
we got a matrix of dims (0, 1) we could make the same available in Rcpp.
More generally, a vector x could be coerced into a matrix of dims (length(x), 1)
(once again just as in R as.matrix())
sourceCpp("/tmp/serguei.cpp")
g(NULL)
Error in g(NULL) : Not a matrix.
g(matrix())
[,1]
[1,] NA
g(vector())
Error in g(vector()) : Not a matrix.
g(integer())
Error in g(integer()) : Not a matrix.
Is this really useful, and can you not use Nullable<> instead?
Sure I can, but as I already said, my thought is to make the code
looking simpler and clearer in this kind of situations where automatic
coercion does sufficient job. Nullable<T> is much more flexible than that
but more expensive in coding on user's side.
Serguei.
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