added abstract declaration

lib/active_relation.rb

@@ -4,8 +4,8 @@ require 'rubygems'
 require 'activesupport'
 require 'activerecord'
 
-require 'active_relation/sql'
 require 'active_relation/extensions'
+require 'active_relation/sql'
 require 'active_relation/predicates'
 require 'active_relation/relations'
 require 'active_relation/engines'

lib/active_relation/extensions.rb

@@ -1,3 +1,4 @@
 require 'active_relation/extensions/object'
+require 'active_relation/extensions/class'
 require 'active_relation/extensions/array'
 require 'active_relation/extensions/hash'

lib/active_relation/extensions/class.rb

@@ -0,0 +1,17 @@
+class Class
+  def abstract(*methods)
+    methods.each do |method|
+      define_method method do
+        raise NotImplementedError
+      end
+    end
+  end
+  
+  def hash_on(delegatee)
+    define_method :eql? do |other|
+      self == other
+    end
+    
+    delegate :hash, :to => delegatee
+  end
+end

lib/active_relation/extensions/object.rb

@@ -1,12 +1,4 @@
-class Object
-  def self.hash_on(delegatee)
-    def eql?(other)
-      self == other
-    end
-    
-    delegate :hash, :to => delegatee
-  end
-  
+class Object  
   def bind(relation)
     ActiveRelation::Value.new(self, relation)
   end

lib/active_relation/sql.rb

@@ -8,6 +8,8 @@ module ActiveRelation
       attr_reader :engine
       include Quoting
       
+      abstract :attribute, :select, :value
+      
       def initialize(engine)
         @engine = engine
       end

spec/active_relation/unit/relations/compound_spec.rb

@@ -21,13 +21,5 @@ module ActiveRelation
         @compound_relation.attributes.should == @relation.attributes.collect { |a| a.bind(@compound_relation) }
       end
     end
-    
-    describe 'hashing' do
-      it 'implements hash equality' do
-        hash = {}
-        hash[@compound_relation] = 1
-        hash[ConcreteCompound.new(@relation)].should == 1
-      end
-    end
   end
 end