Fix R 4.0.0 compatibility problem

[ianmcook]

On 2019-12-04, Kurt Hornik emailed the following:

Dear maintainer,

Please see the problems shown on https://cran.r-project.org/web/checks/check_results_wkb.html.

Specifically, see the problems shown for the r-devel Debian checks.

These can be reproduced by checking with --as-cran using current r-devel, which for now sets

R_CLASS_MATRIX_ARRAY=true

in the check environment, to the effect that

R> class(matrix(1 : 4, 2, 2))
[1] "matrix" "array"

(and no longer just "matrix" as before).

According to the R NEWS file,

For now only active when environment variable R_CLASS_MATRIX_ARRAY
is set to non-empty, but planned to be the new unconditional behavior
when R 4.0.0 is released:

matrix objects now also inherit from class "array", namely, e.g.,
class(diag(1)) is c("matrix", "array") which invalidates code
assuming that length(class(obj)) == 1, an incorrect assumption that
is less frequently fulfilled now.

S3 methods for "array", i.e., .array(), are now also
dispatched for matrix objects.

Apparently your package no longer works correctly when class(matrix(...)) gives a vector of length two: please fix as necessary.

See https://developer.r-project.org/Blog/public/2019/11/09/when-you-think-class.-think-again/index.html for more information about correctly using class() in package code.

Please correct before 2019-12-18 to safely retain your package on CRAN.

[ianmcook]

Fixed in 0cc7c87