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.

6 files changed, 37 insertions, 19 deletions

diff --git a/lib/arel/visitors/depth_first.rb b/lib/arel/visitors/depth_first.rb
index eab20ac831..a434f404c7 100644
--- a/lib/arel/visitors/depth_first.rb
+++ b/lib/arel/visitors/depth_first.rb
@@ -3,6 +3,7 @@ module Arel
     class DepthFirst < Arel::Visitors::Visitor
       def initialize block = nil
         @block = block || Proc.new
+        super()
       end
 
       private
@@ -86,6 +87,7 @@ module Arel
       alias :visit_Arel_Nodes_RightOuterJoin     :binary
       alias :visit_Arel_Nodes_TableAlias         :binary
       alias :visit_Arel_Nodes_Values             :binary
+      alias :visit_Arel_Nodes_Union              :binary
 
       def visit_Arel_Nodes_StringJoin o
         visit o.left
@@ -116,6 +118,8 @@ module Arel
       alias :visit_Arel_Nodes_SqlLiteral         :terminal
       alias :visit_Arel_Nodes_BindParam          :terminal
       alias :visit_Arel_Nodes_Window             :terminal
+      alias :visit_Arel_Nodes_True               :terminal
+      alias :visit_Arel_Nodes_False              :terminal
       alias :visit_BigDecimal                    :terminal
       alias :visit_Bignum                        :terminal
       alias :visit_Class                         :terminal
diff --git a/lib/arel/visitors/dot.rb b/lib/arel/visitors/dot.rb
index 12cce1e266..e0c02d717a 100644
--- a/lib/arel/visitors/dot.rb
+++ b/lib/arel/visitors/dot.rb
@@ -15,6 +15,7 @@ module Arel
       end
 
       def initialize
+        super()
         @nodes      = []
         @edges      = []
         @node_stack = []
diff --git a/lib/arel/visitors/reduce.rb b/lib/arel/visitors/reduce.rb
index 9670cad27c..1d74934fe5 100644
--- a/lib/arel/visitors/reduce.rb
+++ b/lib/arel/visitors/reduce.rb
@@ -10,14 +10,14 @@ module Arel
       private
 
       def visit object, collector
-        send dispatch[object.class], object, collector
+        send dispatch[object.class.name], object, collector
       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
diff --git a/lib/arel/visitors/to_sql.rb b/lib/arel/visitors/to_sql.rb
index dea6830e8f..7bef8feded 100644
--- a/lib/arel/visitors/to_sql.rb
+++ b/lib/arel/visitors/to_sql.rb
@@ -59,8 +59,8 @@ module Arel
       DISTINCT = 'DISTINCT'   # :nodoc:
 
       def initialize connection
+        super()
         @connection     = connection
-        @schema_cache   = connection.schema_cache
       end
 
       def compile node, &block
@@ -69,6 +69,10 @@ module Arel
 
       private
 
+      def schema_cache
+        @connection.schema_cache
+      end
+
       def visit_Arel_Nodes_DeleteStatement o, collector
         collector << "DELETE FROM "
         collector = visit o.relation, collector
@@ -160,7 +164,7 @@ module Arel
       end
 
       def table_exists? name
-        @schema_cache.table_exists? name
+        schema_cache.table_exists? name
       end
 
       def column_for attr
@@ -174,7 +178,7 @@ module Arel
       end
 
       def column_cache(table)
-        @schema_cache.columns_hash(table)
+        schema_cache.columns_hash(table)
       end
 
       def visit_Arel_Nodes_Values o, collector
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
diff --git a/lib/arel/visitors/where_sql.rb b/lib/arel/visitors/where_sql.rb
index 27dde73673..afde15a6c5 100644
--- a/lib/arel/visitors/where_sql.rb
+++ b/lib/arel/visitors/where_sql.rb
@@ -1,6 +1,8 @@
 module Arel
   module Visitors
     class WhereSql < Arel::Visitors::ToSql
+      private
+
       def visit_Arel_Nodes_SelectCore o, collector
         collector << "WHERE "
         inject_join o.wheres, collector, ' AND '