1 files changed, 42 insertions, 15 deletions

diff --git a/lib/sqlalchemy/sql/visitors.py b/lib/sqlalchemy/sql/visitors.py
index 3f06535de..371c6ec4b 100644
--- a/lib/sqlalchemy/sql/visitors.py
+++ b/lib/sqlalchemy/sql/visitors.py
@@ -1,10 +1,39 @@
 from collections import deque
+import re
+from sqlalchemy import util
+
+class VisitableType(type):
+    def __init__(cls, clsname, bases, dict):
+        if not '__visit_name__' in cls.__dict__:
+            m = re.match(r'_?(\w+?)(?:Expression|Clause|Element|$)', clsname)
+            x = m.group(1)
+            x = re.sub(r'(?!^)[A-Z]', lambda m:'_'+m.group(0).lower(), x)
+            cls.__visit_name__ = x.lower()
+        
+        # set up an optimized visit dispatch function
+        # for use by the compiler
+        visit_name = cls.__dict__["__visit_name__"]
+        if isinstance(visit_name, str):
+            func_text = "def _compiler_dispatch(self, visitor, **kw):\n"\
+            "    return visitor.visit_%s(self, **kw)" % visit_name
+        else:
+            func_text = "def _compiler_dispatch(self, visitor, **kw):\n"\
+            "    return getattr(visitor, 'visit_%s' % self.__visit_name__)(self, **kw)"
+    
+        env = locals().copy()
+        exec func_text in env
+        cls._compiler_dispatch = env['_compiler_dispatch']
+        
+        super(VisitableType, cls).__init__(clsname, bases, dict)
+
+class Visitable(object):
+    __metaclass__ = VisitableType
 
 class ClauseVisitor(object):
     __traverse_options__ = {}
     
     def traverse_single(self, obj):
-        for v in self._iterate_visitors:
+        for v in self._visitor_iterator:
             meth = getattr(v, "visit_%s" % obj.__visit_name__, None)
             if meth:
                 return meth(obj)
@@ -17,29 +46,33 @@ class ClauseVisitor(object):
     def traverse(self, obj):
         """traverse and visit the given expression structure."""
 
+        return traverse(obj, self.__traverse_options__, self._visitor_dict)
+    
+    @util.memoized_property
+    def _visitor_dict(self):
         visitors = {}
 
         for name in dir(self):
             if name.startswith('visit_'):
                 visitors[name[6:]] = getattr(self, name)
-            
-        return traverse(obj, self.__traverse_options__, visitors)
-
-    def _iterate_visitors(self):
+        return visitors
+        
+    @property
+    def _visitor_iterator(self):
         """iterate through this visitor and each 'chained' visitor."""
         
         v = self
         while v:
             yield v
             v = getattr(v, '_next', None)
-    _iterate_visitors = property(_iterate_visitors)
 
     def chain(self, visitor):
         """'chain' an additional ClauseVisitor onto this ClauseVisitor.
         
         the chained visitor will receive all visit events after this one.
+        
         """
-        tail = list(self._iterate_visitors)[-1]
+        tail = list(self._visitor_iterator)[-1]
         tail._next = visitor
         return self
 
@@ -52,13 +85,7 @@ class CloningVisitor(ClauseVisitor):
     def traverse(self, obj):
         """traverse and visit the given expression structure."""
 
-        visitors = {}
-
-        for name in dir(self):
-            if name.startswith('visit_'):
-                visitors[name[6:]] = getattr(self, name)
-            
-        return cloned_traverse(obj, self.__traverse_options__, visitors)
+        return cloned_traverse(obj, self.__traverse_options__, self._visitor_dict)
 
 class ReplacingCloningVisitor(CloningVisitor):
     def replace(self, elem):
@@ -74,7 +101,7 @@ class ReplacingCloningVisitor(CloningVisitor):
         """traverse and visit the given expression structure."""
 
         def replace(elem):
-            for v in self._iterate_visitors:
+            for v in self._visitor_iterator:
                 e = v.replace(elem)
                 if e:
                     return e