some drying up of boiler plate initialization and equality code

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/arel/extensions/class.rb b/lib/arel/extensions/class.rb
index 09e6d86ed4..f37898e7d7 100644
--- a/lib/arel/extensions/class.rb
+++ b/lib/arel/extensions/class.rb
@@ -1,4 +1,30 @@
 class Class
+  def attributes(*attrs)
+    @attributes = attrs
+    attr_reader *attrs
+  end
+  
+  def deriving(*methods)
+    methods.each { |m| derive m }
+  end
+  
+  def derive(method_name)
+    methods = {
+      :initialize => "
+        def #{method_name}(#{@attributes.join(',')})
+          #{@attributes.collect { |a| "@#{a} = #{a}" }.join("\n")}
+        end
+      ",
+      :== => "
+        def ==(other)
+          #{name} === other &&
+          #{@attributes.collect { |a| "@#{a} == other.#{a}" }.join(" &&\n")}
+        end
+      "
+    }
+    class_eval methods[method_name], __FILE__, __LINE__
+  end
+  
   def hash_on(delegatee)
     define_method :eql? do |other|
       self == other