access elements deep in a nested enumerable safely

enumerable_try_keys.rb

# Makes it easy to access elements deep within a nested Enumerable. Rather than
# having to do
#
#  enum[:foo] && enum[:foo][:bar]
#
# you can just do
#
#  enum.try_keys :foo, :bar
module Enumerable
  def try_keys *keys
    keys.inject(self) do |target, key|
      (target.respond_to?(:[]) and target[key]) or break
    end
  end
end

describe "an enumerable with try_keys", :shared => true do
  it "should return the value if it exists" do
    @enumerable.try_keys(*@good_keys).should == @expected
  end

  it "should return nil if it doesn't exist" do
    @enumerable.try_keys(*@bad_keys).should be_nil
  end
end

describe "Enumerable#try_keys" do
  describe "with a Hash" do
    before :each do
      @expected = true
      @enumerable = {:foo => {:bar => @expected}}
      @good_keys = [:foo, :bar]
      @bad_keys = [:baz, :bar]
    end
    it_should_behave_like "an enumerable with try_keys"
  end

  describe "with an Array" do
    before :each do
      @expected = true
      @enumerable = [:foo, [:bar, @expected]]
      @good_keys = [1, 1]
      @bad_keys = [0, 1]
    end

    it_should_behave_like "an enumerable with try_keys"
  end

  describe "with an Array of Hashes" do
    before :each do
      @expected = true
      @enumerable = [:foo, {:bar => false, :baz => @expected}]
      @good_keys = [1, :baz]
      @bad_keys = [0, :baz]
    end

    it_should_behave_like "an enumerable with try_keys"
  end
end