implemented hashing macro; implemented custom matcher testing this macro

lib/active_relation/extensions/object.rb

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

lib/active_relation/primitives/attribute.rb

@@ -48,10 +48,7 @@ module ActiveRelation
     
     module Congruence
       def self.included(klass)
-        klass.class_eval do
-          alias_method :eql?, :==
-          delegate :hash, :to => :name
-        end
+        klass.hash_on :name
       end
       
       def history

lib/active_relation/relations/relation.rb

@@ -102,10 +102,6 @@ module ActiveRelation
       false
     end
     
-    def eql?(other)
-      self == other
-    end
-
     def to_sql(strategy = Sql::Relation.new(engine))
       strategy.select [
         "SELECT     #{attributes.collect{ |a| a.to_sql(Sql::Projection.new(engine)) }.join(', ')}",

lib/active_relation/relations/table.rb

@@ -3,7 +3,7 @@ module ActiveRelation
     cattr_accessor :engine
     attr_reader :name, :engine
     
-    delegate :hash, :to => :name
+    hash_on :name
     
     def initialize(name, engine = Table.engine)
       @name, @engine = name.to_s, engine

spec/active_relation/unit/primitives/attribute_spec.rb

@@ -68,6 +68,13 @@ module ActiveRelation
           Attribute.new(@relation, :name).should =~ Attribute.new(@relation, :name, :ancestor => Attribute.new(@relation, :name))
         end
       end
+      
+      describe 'hashing' do
+        it "implements hash equality" do
+          Attribute.new(@relation, 'name').should hash_the_same_as(Attribute.new(@relation, 'name'))
+          Attribute.new(@relation, 'name').should_not hash_the_same_as(Attribute.new(@relation, 'id'))
+        end
+      end
     end
     
     describe '#to_sql' do

spec/active_relation/unit/relations/table_spec.rb

@@ -75,9 +75,8 @@ module ActiveRelation
     
     describe 'hashing' do
       it "implements hash equality" do
-        hash = {}
-        hash[Table.new(:users)] = 1
-        hash[Table.new(:users)].should == 1
+        Table.new(:users).should hash_the_same_as(Table.new(:users))
+        Table.new(:users).should_not hash_the_same_as(Table.new(:photos))
       end
     end
     

spec/matchers/hash_the_same_as.rb

@@ -0,0 +1,26 @@
+module HashTheSameAsMatcher
+  class HashTheSameAs
+    def initialize(expected)
+      @expected = expected
+    end
+    
+    def matches?(target)
+      @target = target
+      hash = {}
+      hash[@expected] = :some_arbitrary_value
+      hash[@target] == :some_arbitrary_value
+    end
+    
+    def failure_message
+      "expected #{@target} to hash the same as #{@expected}; they must be `eql?` and have the same `#hash` value"
+    end
+    
+    def negative_failure_message
+      "expected #{@target} to hash differently than #{@expected}; they must not be `eql?` or have a differing `#hash` values"
+    end
+  end
+  
+  def hash_the_same_as(expected)
+    HashTheSameAs.new(expected)
+  end
+end

spec/spec_helper.rb

@@ -26,7 +26,7 @@ class Hash
 end
 
 Spec::Runner.configure do |config|  
-  config.include(BeLikeMatcher)
+  config.include(BeLikeMatcher, HashTheSameAsMatcher)
   config.mock_with :rr
   config.before do
     ActiveRelation::Table.engine = ActiveRecord::Base.connection