recursive_closed_struct.rb

# RecursiveClosedStruct is similar to OpenStruct, except:
#
# * Immutable. Cannot be changed after instantiation.
# * Raises NoMethodError on undefined methods instead of returning nil.
# * Recursively coerces descendants into a RecursiveClosedStruct.
#
# NoMethodError example:
#   struct = RecursiveClosedStruct.new(key1: "value")
#   struct.key1 # => "value"
#   struct.key2 # => NoMethodError
#
# Respond to example:
#   struct = RecursiveClosedStruct.new(key: "value")
#   struct.respond_to?(:key) # => true
#
# Recursive example:
#   struct = RecursiveClosedStruct.new(one: two: {[{three: "four"]})
#   struct.one.two[0].three # => "four"
class RecursiveClosedStruct
  def initialize(hash)
    @hash = hash
  end

  def values
    @hash.values
  end

private

  def fetch(name)
    @hash.fetch(name) do
      raise NoMethodError.new("undefined method `#{name}' for #{self}")
    end
  end

  def method_missing(name, *)
    object = fetch(name)
    if object.is_a?(Hash)
      self.class.new(object)
    elsif object.is_a?(Array)
      object.map do |value|
        self.class.new(value)
      end
    else
      object
    end
  end

  def respond_to_missing?(name, *)
    @hash.keys.include?(name) || super
  end
end

recursive_closed_struct_spec.rb

require 'spec_helper'

describe RecursiveClosedStruct do
  it 'provides readers from a hash' do
    struct = RecursiveClosedStruct.new(key: 'value')
    struct.key.should eq('value')
  end

  it 'provides respond_to? from a hash' do
    struct = RecursiveClosedStruct.new(key: 'value')
    struct.respond_to?(:key).should be_true
  end

  it 'raises when there is no such key' do
    struct = RecursiveClosedStruct.new(key: 'value')
    -> { struct.other_key }.should raise_error(NoMethodError)
  end

  it 'recurses through array of hashes' do
    struct = RecursiveClosedStruct.new({
      one: [{two: 'three'}]
    })
    struct.one[0].two.should eq('three')
  end

  it 'recurses through hashes' do
    struct = RecursiveClosedStruct.new({
      one: {two: {three: 'four'} }
    })
    struct.one.two.three.should eq('four')
  end

  it 'has values' do
    struct = RecursiveClosedStruct.new({one: 'two', three: 'four'})
    struct.values.should eq(['two', 'four'])
  end
end