visitors can define their own cache strategy for dispatch. fixes #57

3 files changed, 31 insertions, 4 deletions

diff --git a/History.txt b/History.txt
index b5c37193ed..4158f5e968 100644
--- a/History.txt
+++ b/History.txt
@@ -1,3 +1,10 @@
+== 2.1.2 / Unreleased
+
+* Bug Fixes
+
+  * Visitors can define their own cache strategey so caches are not shared.
+    Fixes #57
+
 == 2.1.1 / 2011/05/14
 
 * Bug fixes
diff --git a/lib/arel/visitors/visitor.rb b/lib/arel/visitors/visitor.rb
index c9cdf34adb..8f9dd929e1 100644
--- a/lib/arel/visitors/visitor.rb
+++ b/lib/arel/visitors/visitor.rb
@@ -11,15 +11,19 @@ module Arel
         hash[klass] = "visit_#{(klass.name || '').gsub('::', '_')}"
       end
 
+      def dispatch
+        DISPATCH
+      end
+
       def visit object
-        send DISPATCH[object.class], object
+        send dispatch[object.class], object
       rescue NoMethodError => e
-        raise e if respond_to?(DISPATCH[object.class], true)
+        raise e if respond_to?(dispatch[object.class], true)
         superklass = object.class.ancestors.find { |klass|
-          respond_to?(DISPATCH[klass], true)
+          respond_to?(dispatch[klass], true)
         }
         raise(TypeError, "Cannot visit #{object.class}") unless superklass
-        DISPATCH[object.class] = DISPATCH[superklass]
+        dispatch[object.class] = dispatch[superklass]
         retry
       end
     end
diff --git a/test/visitors/test_to_sql.rb b/test/visitors/test_to_sql.rb
index d046e543e1..b52722ddd6 100644
--- a/test/visitors/test_to_sql.rb
+++ b/test/visitors/test_to_sql.rb
@@ -13,6 +13,22 @@ module Arel
         @attr = @table[:id]
       end
 
+      it 'can define a dispatch method' do
+        visited = false
+        viz = Class.new(Arel::Visitors::Visitor) {
+          define_method(:hello) do |node|
+            visited = true
+          end
+
+          def dispatch
+            { Arel::Table => 'hello' }
+          end
+        }.new
+
+        viz.accept(@table)
+        assert visited, 'hello method was called'
+      end
+
       it "should be thread safe around usage of last_column" do
         visit_integer_column = Thread.new do
           Thread.stop