Add new infrastructure to support greater use of __slots__

* Changed AliasedInsp to use __slots__
* Migrated all of strategy_options to use __slots__ for objects.
  Adds new infrastructure to traversals to support shallow
  copy, to dict and from dict based on internal traversal
  attributes.  Load / _LoadElement then leverage this to
  provide clone / generative / getstate without the need
  for __dict__ or explicit attribute lists.

Doing this change revealed that there are lots of things that
trigger off of whether or not a class has a __visit_name__ attribute.
so to suit that we've gone back to having Visitable, which is
a better name than Traversible at this point  (I think
Traversible is mis-spelled too).

Change-Id: I13d04e494339fac9dbda0b8e78153418abebaf72
References: #7527

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index 74469b035..8ae8f8f65 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -17,6 +17,7 @@ from itertools import zip_longest
 import operator
 import re
 import typing
+from typing import TypeVar
 
 from . import roles
 from . import visitors
@@ -571,11 +572,14 @@ class CompileState:
         return decorate
 
 
+SelfGenerative = TypeVar("SelfGenerative", bound="Generative")
+
+
 class Generative(HasMemoized):
     """Provide a method-chaining pattern in conjunction with the
     @_generative decorator."""
 
-    def _generate(self):
+    def _generate(self: SelfGenerative) -> SelfGenerative:
         skip = self._memoized_keys
         cls = self.__class__
         s = cls.__new__(cls)
@@ -783,6 +787,8 @@ class Options(metaclass=_MetaOptions):
 
 
 class CacheableOptions(Options, HasCacheKey):
+    __slots__ = ()
+
     @hybridmethod
     def _gen_cache_key(self, anon_map, bindparams):
         return HasCacheKey._gen_cache_key(self, anon_map, bindparams)
@@ -797,6 +803,8 @@ class CacheableOptions(Options, HasCacheKey):
 
 
 class ExecutableOption(HasCopyInternals):
+    __slots__ = ()
+
     _annotations = util.EMPTY_DICT
 
     __visit_name__ = "executable_option"