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require 'hashie/hash'
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
# 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
(@properties ||= []) << property_name
(@defaults ||= {})[property_name] = options.delete(:default)
class_eval <<-RUBY
def #{property_name}
self['#{property_name}']
end
def #{property_name}=(val)
self['#{property_name}'] = val
end
RUBY
end
# Get a String array of the currently defined
# properties on this Dash.
def self.properties
@properties.collect{|p| p.to_s}
end
# Check to see if the specified property has already been
# defined.
def self.property?(prop)
properties.include?(prop.to_s)
end
# The default values that have been set for this Dash
def self.defaults
@defaults
end
# Retrieve a value from the Dash (will return the
# property's default value if it hasn't been set).
def [](property_name)
super || self.class.defaults[property_name.to_sym]
end
# Set a value on the Dash in a Hash-like way. Only works
# on pre-existing properties.
def []=(property, value)
if self.class.property?(property)
super
else
raise NoMethodError, 'You may only set pre-defined properties.'
end
end
end
end
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