Order column (option) as a symbol

[leonelgalan]

When setting the order column a string must be used, using a symbol won't work.

Works

acts_as_tree order: 'position'

It doesn't

acts_as_tree order: :position

I don't have a good explanation for why would this be better, other than it feels more natural and it wouldn't take much, changing:

https://github.com/mceachen/closure_tree/blob/master/lib/closure_tree/columns.rb#L71

# c = ct_class.columns_hash[order_option]
c = ct_class.columns_hash[order_option.to_s]

Should work with both strings and symbols.

UPDATE
I'm fairly new to testing, but a failing test could look something like this:

# spec/support/models.rb
class OtherLabel < Label
  acts_as_tree :order => :sort_order
end

# spec/label_spec.rb
  context "OtherLabel" do
    it "should include DeterministicNumericOrdering" do
      OtherLabel.include?(ClosureTree::DeterministicNumericOrdering).should be_true
    end
  end

[mceachen]

OK. I'll do this after I get #49 squared away.

[mceachen]

This is released in 4.0.1.