1 files changed, 32 insertions, 0 deletions
diff --git a/lib/arel/algebra/extensions/class.rb b/lib/arel/algebra/extensions/class.rb
new file mode 100644
index 0000000000..520111b90f
--- /dev/null
+++ b/lib/arel/algebra/extensions/class.rb
@@ -0,0 +1,32 @@
+module Arel
+  module ClassExtensions
+    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
+    
+    Class.send(:include, self)
+  end
+end
+