move the dispatch table to be per-instance

visitors are not shared among threads, so any mutations to the cache
should be OK.  The cache is also pre-populated on construction, but we
should pull that out so we can share the cache among visitors in the
future.

1 files changed, 19 insertions, 12 deletions

diff --git a/lib/arel/visitors/visitor.rb b/lib/arel/visitors/visitor.rb
index 0730c15794..2317d0c95f 100644
--- a/lib/arel/visitors/visitor.rb
+++ b/lib/arel/visitors/visitor.rb
@@ -1,32 +1,39 @@
 module Arel
   module Visitors
     class Visitor
+      def initialize
+        @dispatch = Hash.new do |hash, class_name|
+          raise if class_name == 'Arel::Nodes::Union'
+           hash[class_name] = "visit_#{(class_name || '').gsub('::', '_')}"
+        end
+
+        # pre-populate cache. FIXME: this should be passed in to each
+        # instance, but we can do that later.
+        self.class.private_instance_methods.sort.each do |name|
+          next unless name =~ /^visit_(.*)$/
+          @dispatch[$1.gsub('_', '::')] = name
+        end
+      end
+
       def accept object
         visit object
       end
 
       private
 
-      DISPATCH = Hash.new do |hash, visitor_class|
-        hash[visitor_class] =
-          Hash.new do |method_hash, node_class|
-            method_hash[node_class] = "visit_#{(node_class.name || '').gsub('::', '_')}"
-          end
-      end
-
       def dispatch
-        DISPATCH[self.class]
+        @dispatch
       end
 
       def visit object
-        send dispatch[object.class], object
+        send dispatch[object.class.name], object
       rescue NoMethodError => e
-        raise e if respond_to?(dispatch[object.class], true)
+        raise e if respond_to?(dispatch[object.class.name], true)
         superklass = object.class.ancestors.find { |klass|
-          respond_to?(dispatch[klass], true)
+          respond_to?(dispatch[klass.name], true)
         }
         raise(TypeError, "Cannot visit #{object.class}") unless superklass
-        dispatch[object.class] = dispatch[superklass]
+        dispatch[object.class.name] = dispatch[superklass.name]
         retry
       end
     end