Merge pull request rails#204 from trptcolin/visitor_dispatch_caching

Cache visitor dispatch on a per-visitor basis

lib/arel/visitors/visitor.rb

@@ -7,12 +7,15 @@ def accept object
 
       private
 
-      DISPATCH = Hash.new do |hash, klass|
-        hash[klass] = "visit_#{(klass.name || '').gsub('::', '_')}"
+      DISPATCH = Hash.new do |hash, visitor_class|
+        hash[visitor_class] =
+          Hash.new do |hash, node_class|
+            hash[node_class] = "visit_#{(node_class.name || '').gsub('::', '_')}"
+          end
       end
 
       def dispatch
-        DISPATCH
+        DISPATCH[self.class]
       end
 
       def visit object, attribute = nil

test/visitors/test_dispatch_contamination.rb

@@ -0,0 +1,22 @@
+require 'helper'
+
+module Arel
+  module Visitors
+    describe 'avoiding contamination between visitor dispatch tables' do
+      before do
+        @connection = Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      it 'dispatches properly after failing upwards' do
+        node = Nodes::Union.new(Nodes::True.new, Nodes::False.new)
+        assert_equal "( TRUE UNION FALSE )", node.to_sql
+
+        node.first # from Nodes::Node's Enumerable mixin
+
+        assert_equal "( TRUE UNION FALSE )", node.to_sql
+      end
+    end
+  end
+end
+