This is a bug which breaks some array-like behavor for set. The #resizable method should return true for "objects whose size can be changed". Currently:

• Array.resizable? #=> true
• Array.new#resizable? #=> true
• Set.resizable? #=> false (should be true)
• Set.new#resizable? #=> false (should be true)

Note that Set's size can be changed, for instance:

s = Set[1, 2]

s << 3  #=> #<Set: {1, 2, 3}>