NestedStruct

nested_struct.rb

# evolved from http://stackoverflow.com/questions/4911807/cannot-access-id-field-of-openstruct-instance
class NestedStruct
  def initialize( hash= {})
    hash.each{ |key, value| add_field(key,value) }
  end
  
  def add_field( attribute_name, value=nil )
    (class << self; self; end).class_eval do
      attr_accessor attribute_name 
    end
    value = NestedStruct.new(value) if value.class == Hash 
    self.send(attribute_name.to_s + "=", value)
  end
  
def []=( name, value )
    add_field(name,value)
  end
end

nested_struct_spec.rb

describe NestedStruct do
  before do
    @dog = NestedStruct.new
  end
   
  it "can be initialized with a nested hash" do
    nested_struct = NestedStruct.new({:foo => :bar, :a => {:b => "nested value"}})
    nested_struct.foo.should == :bar
    nested_struct.a.b.should == "nested value"
  end
  
  it "can do multi-level attribute nesting" do
    nested_struct = NestedStruct.new({:a => {:b => {:c => "nested value"}}})
    nested_struct.a.b.c.should == "nested value"
  end
  
  it "can be created without pre-defining the struct keys" do
    @dog.class.should == NestedStruct 
  end

  it "can define struct keys after the fact with []" do
    @dog[:bark]= "woof"
    @dog.bark.should == "woof"
  end

  it "can set an #id attribute" do
    @dog[:id] = "abc123"
    @dog.id.should == "abc123"
  end
end