Hash
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.
# File lib/hashie/dash.rb, line 67 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
You may initialize a Dash with an attributes hash just like you would many other kinds of data objects.
# File lib/hashie/dash.rb, line 89 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
Defines a property on the Dash. Options are as follows:
:default - Specify a default value for this property, to be returned before a value is set on the property in a new Dash.
:required - Specify the value as required for this property, to raise an error if a value is unset in a new or existing Dash.
# File lib/hashie/dash.rb, line 30 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 def #{property_name}(&block) self.[](#{property_name.to_s.inspect}, &block) end def #{property_name}=(value) self.[]=(#{property_name.to_s.inspect}, value) end end if defined? @subclasses @subclasses.each { |klass| klass.property(property_name, options) } end required_properties << property_name if options.delete(:required) end
Retrieve a value from the Dash (will return the property's default value if it hasn't been set).
# File lib/hashie/dash.rb, line 110 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.
# File lib/hashie/dash.rb, line 124 def []=(property, value) assert_property_required! property, value assert_property_exists! property super(property.to_s, value) end
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