Removed positional distance resolution.

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## Unreleased
+### Removed
+* Resolving ambiguity using positional distance
 
 ## [1.12](https://pypi.org/project/multimethod/1.12/) - 2024-07-04
 ### Changed

multimethod/__init__.py

@@ -111,7 +111,7 @@ def __subclasscheck__(self, subclass):
 
     def __instancecheck__(self, instance):
         if self.__origin__ is Literal:
-            return any(type(arg) == type(instance) and arg == instance for arg in self.__args__)
+            return any(type(arg) is type(instance) and arg == instance for arg in self.__args__)
         if self.__origin__ is Union:
             return isinstance(instance, self.__args__)
         if hasattr(instance, '__orig_class__'):  # user-defined generic type
@@ -186,14 +186,6 @@ def __and__(self, other):
 subtype.origins.register(parametric, lambda cls: cls.__bases__)
 
 
-def distance(cls, subclass: type) -> int:
-    """Return estimated distance between classes for tie-breaking."""
-    if get_origin(cls) is Union:
-        return min(distance(arg, subclass) for arg in cls.__args__)
-    mro = get_mro(subclass)
-    return mro.index(cls if cls in mro else object)
-
-
 class signature(tuple):
     """A tuple of types that supports partial ordering."""
 
@@ -229,14 +221,6 @@ def __le__(self, other: tuple) -> bool:
     def __lt__(self, other: tuple) -> bool:
         return self != other and self <= other
 
-    def __sub__(self, other: tuple) -> tuple:
-        """Return relative distances, assuming self >= other."""
-        return tuple(map(distance, other, self))
-
-    def __rsub__(self, other: tuple) -> tuple:
-        """Return relative distances, assuming self <= other."""
-        return tuple(map(distance, self, other))
-
     def callable(self, *types) -> bool:
         """Check positional arity of associated function signature."""
         try:
@@ -339,14 +323,6 @@ def __delitem__(self, types: tuple):
     def select(self, types: tuple, keys: set[signature]) -> Callable:
         keys = {key for key in keys if key.callable(*types)}
         funcs = {self[key] for key in keys}
-        if len(funcs) > 1:
-            groups = collections.defaultdict(set)
-            for key in keys:
-                groups[types - key].add(key)
-            keys = groups[min(groups)]
-            funcs = {self[key] for key in keys}
-            if len(funcs) == 1:
-                warnings.warn("positional distance tie-breaking is deprecated", DeprecationWarning)
         if len(funcs) == 1:
             return funcs.pop()
         raise DispatchError(f"{self.__name__}: {len(keys)} methods found", types, keys)

tests/test_methods.py

@@ -43,8 +43,10 @@ def test_join():
     assert join(seq, sep) == '0<>[1]<>2'
     assert join(tree(seq), sep) == '0<>1<>2'
     assert join(seq, bracket(*sep)) == '<0><[1]><2>'
-    with pytest.warns(DeprecationWarning):
+    with pytest.raises(DispatchError):
         assert join(tree(seq), bracket(*sep)) == '<0><1><2>'
+    join[tree, bracket] = join[tree, object]
+    assert join(tree(seq), bracket(*sep)) == '<0><1><2>'
 
 
 def subclass(*bases, **kwds):
@@ -83,19 +85,9 @@ def test_signature():
     assert signature([Any, list, NewType('', int)]) == (object, list, int)
     assert signature([AnyStr]) == signature([Union[bytes, str]])
     assert signature([TypeVar('T')]) == signature([object])
-    assert signature([int]) - signature([Union[int, float]]) == (0,)
     assert signature([list]) <= (list,)
     assert signature([list]) <= signature([list])
     assert signature([list]) <= signature([list[int]])
-    assert signature([list[int]]) - signature([list])
-    assert signature([list]) - signature([list[int]]) == (1,)
-
-    # with metaclasses:
-    assert signature([type]) - (type,) == (0,)
-    assert (type,) - signature([object]) == (1,)
-    # using EnumMeta because it is a standard, stable, metaclass
-    assert signature([enum.EnumMeta]) - signature([object]) == (2,)
-    assert signature([Union[type, enum.EnumMeta]]) - signature([object]) == (1,)
 
 
 class namespace:

tests/test_subscripts.py

@@ -5,7 +5,7 @@
 from array import array
 from collections.abc import Callable, Iterable, Mapping, Sequence
 from typing import Generic, Literal, Type, TypeVar, Union
-from multimethod import distance, multimethod, parametric, subtype, DispatchError
+from multimethod import multimethod, parametric, subtype, DispatchError
 
 
 def test_literals():
@@ -65,7 +65,6 @@ class cls(Generic[TypeVar('T')]):
     def func(x: cls[int]):
         pass
 
-    assert distance(object, cls[int])
     obj = cls[int]()
     assert isinstance(obj, subtype(cls[int]))
     assert func(obj) is None