MappedHash

mapped_hash.rb

class MappedHash < Hash
  attr_writer :mappings

  def mappings
    @mappings || {}
  end

  def [](name)
    super || super(mappings[name])
  end

  def self.from_hash(hash)
    new.tap do |mapped_hash|
      hash.each { |key, value| mapped_hash[key] = value }
    end
  end

end

mapped_hash_spec.rb

require File.expand_path('mapped_hash')

describe MappedHash do

  shared_examples_for "an existing hash key" do

    it { should be_nil }

    context "when the 'foo' attribute is set to 'baz'" do

      before { mapped_hash[:foo] = 'baz' }

      it { should == 'baz' }

    end

  end

  let(:mapped_hash) { MappedHash.new }

  describe "#mappings" do

    subject { mapped_hash.mappings }

    it { should == {} }

    context "after adding `:name => 'Naam'` as a mapping" do

      before { mapped_hash.mappings = {:name => 'Naam'} }

      it { should == {:name => 'Naam'} }

    end

  end

  describe "#[:foo]" do

    subject { mapped_hash[:foo] }

    it_should_behave_like 'an existing hash key'

  end

  describe "#[:bar] (mapped to foo)" do

    before { mapped_hash.mappings = {:bar => :foo} }

    subject { mapped_hash[:bar] }

    it_should_behave_like 'an existing hash key'

  end

  describe ".from_hash" do

    context "when passing an empty hash" do

      subject { MappedHash.from_hash({}) }

      it { should be_empty }

    end

    context "when passing a hash with a value" do

      let(:mapped_hash) { MappedHash.from_hash({:foo => 'bar'}) }

      subject { mapped_hash }

      it { should have_key :foo }

      describe "the value of :foo" do

        subject { mapped_hash[:foo] }

        it { should == 'bar' }

      end

    end

  end

end

ugly_dutch_hash.rb

class UglyDutchHash < MappedHash

  def mappings
    {
      :name => 'Naam'
    }
  end

end

# h = UglyDutchHash.from_hash({'Naam' => 'Barrie'})
# => {"Naam"=>"Barrie"}
# h[:name]
# => "Barrie"