created new Hashie type Lash

1 files changed, 89 insertions, 0 deletions

diff --git a/lib/hashie/lash.rb b/lib/hashie/lash.rb
new file mode 100644
index 0000000..72cb5c9
--- /dev/null
+++ b/lib/hashie/lash.rb
@@ -0,0 +1,89 @@
+require 'hashie/dash'
+
+module Hashie
+  # A Lash is just like a Dash, except that a Lash allows
+  # that properties can set as required. This means that if
+  # an attempt is made to create a Lash with out it, an error
+  # will be raised.
+  #
+  # 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, and
+  # certain attributes are required.
+  #
+  # It is preferrable to a Struct because of the in-class
+  # API for defining properties as well as per-property defaults
+  # and requirements.
+  class Lash < Hashie::Dash
+
+    # Defines a property on the Lash. 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
+    #   Lash.
+    #
+    # * <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 Lash.
+    #
+    def self.property(property_name, options = {})
+      super
+      required_properties << property_name if options.delete(:required)
+    end
+
+    class << self
+      attr_reader :required_properties
+    end
+    instance_variable_set('@required_properties', Set.new)
+
+    def self.inherited(klass)
+      super
+      klass.instance_variable_set('@required_properties', self.required_properties.dup)
+    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 Lash with an attributes hash
+    # just like you would many other kinds of data objects.
+    # Remember to pass in the values for the properties
+    # you set as required.
+    def initialize(attributes = {}, &block)
+      super(attributes, &block)
+      assert_required_properties_set!
+    end
+
+    # Set a value on the Lash in a Hash-like way. Only works
+    # on pre-existing properties and errors if you try to
+    # set a required value to nil.
+    def []=(property, value)
+      assert_property_required! property, value
+      super(property.to_s, value)
+    end
+
+
+    private
+
+      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 Lash."
+        end
+      end
+
+      def assert_property_required!(property, value)
+        if self.class.required?(property) && value.nil?
+          raise ArgumentError, "The property '#{property}' is required for this Lash."
+        end
+      end
+  end
+end