From: Joel VanderWerf <joelvanderwerf@...>
Date: 2010-07-14T07:09:34+09:00
Subject: Re: Ruby garabage collector

Abder-Rahman Ali wrote:
> In the "Why's poignant guide to Ruby" book, it states the following:
> 
> "If you can't get to an object through a variable, then Ruby will figure
> you are done with it and will get rid of it. Periodically, Ruby sends
> out its garbage collector to set these objects free."
> 
> The point I'm not getting here is: "If you can't get to an object
> through a variable..."
> 
> Can you provide an examples that illustrates this?

Here's an example to play with:

class C; end

def make_one
   $c = C.new
   nil # Can you guess why this is here?
end

def clear!
   $c = nil
end

# How many reachable C instances are there?
#  (Note: works in MRI, but maybe not others, such as jruby)
def how_many?
   p ObjectSpace.each_object(C) {}
end

GC.start
how_many?  # => 0
make_one
how_many?  # => 1
make_one
how_many?  # => 2
clear!
how_many?  # => 2
GC.start
how_many?  # => 0

-----


As Rick pointed out ("variables don't get collected, objects do"), the 
question of variable scope is not really the important one. In the above 
example, $c is always in scope, because it is a global. What's important 
is whether an object can be reached from the value assigned to $c.