Ruby Array Extension -

my prep work asking me make array extension file , add methods it. gave me:

describe array    describe "#sum"     "has #sum method"       [].should respond_to(:sum)     end      "should 0 empty array"       [].sum.should == 0     end      "should add of elements"       [1,2,4].sum.should == 7     end   end end 

so i've written this:

class array     def sum(array = [])         add = 0         if array == []             array = add       else             while array.length > 0             add = add + array.last             array.pop             end             array = add         end         array     end  end 

i keep getting error:

array   #sum     has #sum method     should 0 empty array     should add of elements (failed - 1)  failures:    1) array#sum should add of elements      failure/error: [1,2,4].sum.should == 7        expected: 7             got: 0 (using ==)      # ./14_array_extensions/array_extensions_spec.rb:23:in `block (3 levels) in <top (required)>'  finished in 0.00241 seconds 3 examples, 1 failure 

thanks time.

extending array means should using self rather passing in array. right now, you're summing empty array (from default parameter) rather array #sum called on.