Hi gurus, I've found a weird effect when trying to track down a memory leak in a Rails app. Can anyone explain what's going on here?

Save this script as a plain Ruby script (Rails not necessary):

class Fnord
    def to_s
        'fnord'
    end
end

def test
    f = Fnord.new
end

test

GC.start
sleep 2

ObjectSpace.each_object do |o|
    puts o if o.is_a? Fnord
end

When I run this via

ruby 1.8.7 (2009-06-12 patchlevel 174) [i486-linux]

I get the following:

bash $ ruby var_test
fnord

Although the variable f is out of scope, there are no other references to the single Fnord object, and I've garbage collected, the object still seems to exist. Is this a nefarious memory leak of some sort, or am I completely missing something about Ruby?

Further, if I change the test method to this:

def test
    f = Fnord.new
    f = nil
end

I get no output. But surely this should not change the semantics here?

Many thanks!