Question

In Rebol 2 you could check for an empty bitset with EMPTY?

>> empty? make bitset! #{00}
== true

In Rebol 3 (Build 21-Feb-2011/0:44:24) this is not the case.

>> empty? make bitset! #{00}
== false

Bug or new behavior? Either way, how else might I do this test? Empty bitsets of different sizes do not compare as equal in either R2 or R3:

>> (make bitset! #{00}) == (make bitset! #{0000})
== false

Answer 1

New behaviour: a bitset with >0 bits is not empty; even if it has no bits set, it still contains cleared bits.

In R3, you can or a given bitset with the empty bitset, to find out if the first is empty — that is: it has no bits set — as well:

>> empty? (make bitset! #{00}) or (make bitset! #{})
== true

>> empty? (make bitset! #{0000}) or (make bitset! #{})
== true

As a convenient shortcut, you can also just or with an empty binary!, enabling the following definition:

bitset-clear?: func [bitset [bitset!]] [empty? bitset or #{}]

Again, using your examples:

>> bitset-clear? make bitset! #{00}   
== true

>> bitset-clear? make bitset! #{0000}
== true