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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 < Hash
include 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.
#
# * <tt>:required</tt> - Specify the value as required for this
# property, to raise an error if a value is unset in a new or
# existing Dash.
#
def self.property(property_name, options = {})
property_name = property_name.to_sym
self.properties << property_name
if options.has_key?(:default)
self.defaults[property_name] = options[:default]
elsif self.defaults.has_key?(property_name)
self.defaults.delete property_name
end
unless instance_methods.map { |m| m.to_s }.include?("#{property_name}=")
class_eval <<-ACCESSORS
def #{property_name}(&block)
self.[](#{property_name.to_s.inspect}, &block)
end
def #{property_name}=(value)
self.[]=(#{property_name.to_s.inspect}, value)
end
ACCESSORS
end
if defined? @subclasses
@subclasses.each { |klass| klass.property(property_name, options) }
end
required_properties << property_name if options.delete(:required)
end
class << self
attr_reader :properties, :defaults
attr_reader :required_properties
end
instance_variable_set('@properties', Set.new)
instance_variable_set('@defaults', {})
instance_variable_set('@required_properties', Set.new)
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)
klass.instance_variable_set('@required_properties', self.required_properties.dup)
end
# Check to see if the specified property has already been
# defined.
def self.property?(name)
properties.include? name.to_sym
end
# Check to see if the specified property is
# required.
def self.required?(name)
required_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[prop] = begin
value.dup
rescue TypeError
value
end
end
initialize_attributes(attributes)
assert_required_properties_set!
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
value = super(property.to_s)
# If the value is a lambda, proc, or whatever answers to call, eval the thing!
if value.is_a? Proc
self[property] = value.call # Set the result of the call as a value
else
yield value if block_given?
value
end
end
# Set a value on the Dash in a Hash-like way. Only works
# on pre-existing properties.
def []=(property, value)
assert_property_required! property, value
assert_property_exists! property
super(property.to_s, value)
end
def replace(other_hash)
other_hash = self.class.defaults.merge(other_hash)
(keys - other_hash.keys).each { |key| delete(key) }
other_hash.each { |key, value| self[key] = value }
self
end
private
def initialize_attributes(attributes)
attributes.each_pair do |att, value|
self[att] = value
end if attributes
end
def assert_property_exists!(property)
unless self.class.property?(property)
raise NoMethodError, "The property '#{property}' is not defined for this Dash."
end
end
def assert_required_properties_set!
self.class.required_properties.each do |required_property|
assert_property_set!(required_property)
end
end
def assert_property_set!(property)
if send(property).nil?
raise ArgumentError, "The property '#{property}' is required for this Dash."
end
end
def assert_property_required!(property, value)
if self.class.required?(property) && value.nil?
raise ArgumentError, "The property '#{property}' is required for this Dash."
end
end
end
end
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