From: ball <chezball@...>
Date: 2009-04-30T08:40:12+09:00
Subject: object scope and cleanup

I am having trouble understanding Ruby object cleanup wrt scope. In
particular, I would think that an object is getting deleted, but it
turns out that is not the case. I have an RSpec test below. The
BinarySearchTree size is defined as:

  def size
    @count = ObjectSpace.each_object(TreeNode) {}
  end

I have the following Spec code:

describe BinarySearchTree do

  it "should have size ZERO to start with" do
    @tree = BinarySearchTree.new
    @tree.size.should == 0
  end

  it "should have a size of ONE when we insert an item" do
    @tree = BinarySearchTree.new
    @tree.insert(5);
    @tree.size.should == 1
  end

  it "should have a size of TWO when we insert two items" do
    @tree = BinarySearchTree.new
    @tree.insert(5);
    @tree.insert(3);
    @tree.size.should == 2
  end
end


And the problem is, that when I get to the last assertion,
>>     @tree.size.should == 2

It fails, saying that there are 3 objects (not 2). Presumably because
the previous BinarySearchTree didn't delete the TreeNode.

Can you explain why?
And what can I do about it? (including "don't use ObjectSpace that
way")