R devel - Apr 2016 - Bounds error when indexing a matrix with NA_character_

Hi!


I've just got a bounds error when trying to index a matrix with
NA_character_:
> y <- matrix(1:4, 2, 2, dimnames = list(A=c("a",
"b"), B=c("a", "b")))
> y[NA,]
??????B
A???????a??b
? <NA> NA NA
? <NA> NA NA
> y[NA_integer_,]
?a?
?b?
NA NA?
> y[NA_character_,]
Error in y[NA_character_, ] : index out of
bounds


Yet, I would have sworn it behaves like integer NA (which apparently
isn't true since it also occurs with R 3.0). Assuming this isn't simply
a bug, what's the rationale behind this, and is it documented anywhere?
For example, ?Extract says:
> ?????When extracting, a numerical, logical or character ?NA? index
> ?????picks an unknown element and so returns ?NA? in the corresponding
> ?????element of a logical, integer, numeric, complex or character
> ?????result, and ?NULL? for a list.??(It returns ?00? for a raw
> ?????result.)
An indeed that's how it works for vectors:
> x <- c(a=1)
> x[NA_character_]
<NA>?
? NA?

The inconsistency between NA classes, and between vectors and matrices
is surprising.


Thanks for your comments.