base class works with visitor

History.txt

@@ -1,5 +1,10 @@
 == 2.0.5 (unreleased)
 
+* Enhancements
+
+  * Arel::Visitors::DepthFirst can walk your AST depth first
+  * Arel::Nodes::Node is enumerable, depth first
+
 * Bug fixes
 
   * #lock will lock SELECT statements "FOR UPDATE" on mysql

lib/arel/nodes/node.rb

@@ -37,6 +37,8 @@ module Arel
 
       # Iterate through AST, nodes will be yielded depth-first
       def each &block
+        return enum_for(:each) unless block_given?
+
         Visitors::DepthFirst.new(block).accept self
       end
     end

lib/arel/visitors/depth_first.rb

@@ -93,6 +93,7 @@ module Arel
       alias :visit_ActiveSupport_Multibyte_Chars :terminal
       alias :visit_ActiveSupport_StringInquirer  :terminal
       alias :visit_Arel_Nodes_Lock               :terminal
+      alias :visit_Arel_Nodes_Node               :terminal
       alias :visit_Arel_Nodes_SqlLiteral         :terminal
       alias :visit_Arel_SqlLiteral               :terminal
       alias :visit_BigDecimal                    :terminal

test/visitors/test_depth_first.rb

@@ -192,6 +192,12 @@ module Arel
         @visitor.accept stmt
         assert_equal [:a, :b, stmt.columns, :c, stmt], @collector.calls
       end
+
+      def test_node
+        node = Nodes::Node.new
+        @visitor.accept node
+        assert_equal [node], @collector.calls
+      end
     end
   end
 end