1 files changed, 42 insertions, 0 deletions
diff --git a/activerecord/lib/arel/visitors/visitor.rb b/activerecord/lib/arel/visitors/visitor.rb
new file mode 100644
index 0000000000..1c17184e86
--- /dev/null
+++ b/activerecord/lib/arel/visitors/visitor.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Visitor
+      def initialize
+        @dispatch = get_dispatch_cache
+      end
+
+      def accept(object, *args)
+        visit object, *args
+      end
+
+      private
+
+        attr_reader :dispatch
+
+        def self.dispatch_cache
+          Hash.new do |hash, klass|
+            hash[klass] = "visit_#{(klass.name || '').gsub('::', '_')}"
+          end
+        end
+
+        def get_dispatch_cache
+          self.class.dispatch_cache
+        end
+
+        def visit(object, *args)
+          dispatch_method = dispatch[object.class]
+          send dispatch_method, object, *args
+        rescue NoMethodError => e
+          raise e if respond_to?(dispatch_method, true)
+          superklass = object.class.ancestors.find { |klass|
+            respond_to?(dispatch[klass], true)
+          }
+          raise(TypeError, "Cannot visit #{object.class}") unless superklass
+          dispatch[object.class] = dispatch[superklass]
+          retry
+        end
+    end
+  end
+end