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require 'hashie/hash'
require 'set'
module Hashie
# A Dash is a 'defined' or 'discrete' Hash, that is, a Hash
# that has a set of defined keys that are accessible (with
# optional defaults) and only those keys may be set or read.
#
# Dashes are useful when you need to create a very simple
# lightweight data object that needs even fewer options and
# resources than something like a DataMapper resource.
#
# It is preferrable to a Struct because of the in-class
# API for defining properties as well as per-property defaults.
class Dash < Hashie::Hash
include Hashie::PrettyInspect
alias_method :to_s, :inspect
# Defines a property on the Dash. Options are
# as follows:
#
# * <tt>:default</tt> - Specify a default value for this property,
# to be returned before a value is set on the property in a new
# Dash.
#
def self.property(property_name, options = {})
property_name = property_name.to_sym
self.properties << property_name
if options[:default] or self.defaults[property_name]
self.defaults[property_name] = options[:default]
end
unless instance_methods.map { |m| m.to_s }.include?("#{property_name}=")
class_eval <<-ACCESSORS
def #{property_name}
_regular_reader(#{property_name.to_s.inspect})
end
def #{property_name}=(value)
_regular_writer(#{property_name.to_s.inspect}, value)
end
ACCESSORS
end
if defined? @subclasses
@subclasses.each { |klass| klass.property(property_name, options) }
end
end
class << self
attr_reader :properties, :defaults
end
instance_variable_set('@properties', Set.new)
instance_variable_set('@defaults', {})
def self.inherited(klass)
super
(@subclasses ||= Set.new) << klass
klass.instance_variable_set('@properties', self.properties.dup)
klass.instance_variable_set('@defaults', self.defaults.dup)
end
# Check to see if the specified property has already been
# defined.
def self.property?(name)
properties.include? name.to_sym
end
# You may initialize a Dash with an attributes hash
# just like you would many other kinds of data objects.
def initialize(attributes = {}, &block)
super(&block)
self.class.defaults.each_pair do |prop, value|
self.send("#{prop}=", value)
end
attributes.each_pair do |att, value|
self[att] = value
end if attributes
end
alias_method :_regular_reader, :[]
alias_method :_regular_writer, :[]=
private :_regular_reader, :_regular_writer
# Retrieve a value from the Dash (will return the
# property's default value if it hasn't been set).
def [](property)
assert_property_exists! property
super(property.to_s)
end
# Set a value on the Dash in a Hash-like way. Only works
# on pre-existing properties.
def []=(property, value)
assert_property_exists! property
super(property.to_s, value)
end
private
def assert_property_exists!(property)
unless self.class.property?(property)
raise NoMethodError, "The property '#{property}' is not defined for this Dash."
end
end
end
end
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