Make Variable@dims <- NULL reset to scalar

The dims setter early-returned on empty input, so resetting a variable
to scalar (NULL dims, per the class's own convention) silently kept the
stale dims. r2f-assign.R's deferred-mode path assigns
`var@dims <- value@value@dims` with a legitimately-NULL RHS and relied
on this working. Assign the attribute directly (the same S7 workaround
already used by the `r` property) to avoid recursing through the setter.

Author: mns-nordicals

R/classes.R

@@ -240,6 +240,9 @@ Variable := new_class(
       NULL | class_list,
       setter = function(self, value) {
         if (!length(value)) {
+          # reset to scalar (NULL means scalar); assign the attribute
+          # directly to avoid recursing through this setter
+          attr(self, "dims") <- NULL
           return(self)
         }
 

tests/testthat/test-classes.R

@@ -109,3 +109,11 @@ test_that("new_setter errors for invalid coerce argument", {
     "coerce must be TRUE, FALSE, NULL"
   )
 })
+
+test_that("Variable@dims can be reset to scalar with NULL", {
+  v <- quickr:::Variable("double", list(2L, 3L))
+  expect_identical(v@dims, list(2L, 3L))
+  v@dims <- NULL
+  expect_null(v@dims)
+  expect_true(v@is_scalar)
+})