class Hashie::Dash
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.
Attributes
Public Class Methods
# 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 newDash
. -
:required
- Specify the value as required for this property, to raise an error if a value is unset in a new or existingDash
.
# 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 <<-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
Check to see if the specified property has already been defined.
# File lib/hashie/dash.rb, line 77 def self.property?(name) properties.include? name.to_sym end
Check to see if the specified property is required.
# File lib/hashie/dash.rb, line 83 def self.required?(name) required_properties.include? name.to_sym end
Public Instance Methods
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
# File lib/hashie/dash.rb, line 130 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 Instance Methods
# File lib/hashie/dash.rb, line 145 def assert_property_exists!(property) unless self.class.property?(property) raise NoMethodError, "The property '#{property}' is not defined for this Dash." end end
# File lib/hashie/dash.rb, line 163 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
# File lib/hashie/dash.rb, line 157 def assert_property_set!(property) if send(property).nil? raise ArgumentError, "The property '#{property}' is required for this Dash." end end
# File lib/hashie/dash.rb, line 151 def assert_required_properties_set! self.class.required_properties.each do |required_property| assert_property_set!(required_property) end end
# File lib/hashie/dash.rb, line 139 def initialize_attributes(attributes) attributes.each_pair do |att, value| self[att] = value end if attributes end