Recursive Ruby data structure diff

object_comparison_helper.rb

module ObjectComparisonHelper
  def deep_hash_diff(obj1, obj2, path = 'root', differences = [])
    if obj1.class != obj2.class
      differences << "object types differ at #{path}: #{obj1.class} vs #{obj2.class}"
    else
      case obj1
        when Hash, HashWithIndifferentAccess
          differences << "key sets differ at #{path}: #{obj1.keys.inspect} vs #{obj2.keys.inspect}" if obj1.keys.to_set != obj2.keys.to_set
          obj1.each do |key, value|
            deep_hash_diff(value, obj2[key], "#{path}.#{key}", differences)
          end
        when Array
          differences << "array lengths differ at #{path}: #{obj1.length} vs #{obj2.length}" if obj1.length != obj2.length
          obj1.zip(obj2).each.with_index do |(item1, item2), index|
            deep_hash_diff(item1, item2, "#{path}[#{index}]", differences)
          end
        else
          differences << "values differ at #{path}: #{obj1} vs #{obj2}" if obj1 != obj2
      end
    end

    differences
  end
end

object_comparison_helper_spec.rb

require 'spec_helper'

describe ObjectComparisonHelpers do
  let(:helper) do
    Class.new { include ObjectComparisonHelpers }.new
  end

  describe '#deep_hash_diff' do
    it 'outputs an array of difference information' do
      obj1 = {
        'key' => 'value',
        :hash => { foo: :bar, counter: 1 },
        :type => Time.now,
        :array => [1,2,3]
      }

      obj2 = {
        'key' => 'value',
        :hash => { foo: :bar, counter: 2 },
        :type => 'string',
        :array => [1,2,3,4],
        'spurious' => 'value'
      }

      helper.deep_hash_diff(obj1, obj2).should == [
        "key sets differ at root: [\"key\", :hash, :type, :array] vs [\"key\", :hash, :type, :array, \"spurious\"]",
        "values differ at root.hash.counter: 1 vs 2",
        "object types differ at root.type: Time vs String",
        "array lengths differ at root.array: 3 vs 4"
      ]
    end
  end
end