Generalize Dispatcher class

torcharrow/dispatcher.py

@@ -4,7 +4,7 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
-from typing import Callable, ClassVar, Dict, Tuple
+from typing import Callable, ClassVar, Dict, Generic, Tuple, TypeVar
 
 # ---------------------------------------------------------------------------
 # column factory (class methods only!)
@@ -13,21 +13,24 @@
 Typecode = str  # one of dtype.typecode
 
 
-class Dispatcher:
+T = TypeVar("T")
 
-    # singelton, append only, registering is idempotent
-    _calls: ClassVar[Dict[Tuple[Typecode, Device], Callable]] = {}
 
-    @classmethod
-    def register(cls, key: Tuple[Typecode, Device], call: Callable):
-        # key is tuple: (device,typecode)
-        if key in Dispatcher._calls:
-            if call == Dispatcher._calls[key]:
+class _Dispatcher(Generic[T]):
+    def __init__(self):
+        # append only, registering is idempotent
+        self._calls: Dict[T, Callable] = {}
+
+    def register(self, key: T, call: Callable):
+        if key in self._calls:
+            if call == self._calls[key]:
                 return
             else:
                 raise ValueError("keys for calls can only be registered once")
-        Dispatcher._calls[key] = call
+        self._calls[key] = call
+
+    def lookup(self, key: T) -> Callable:
+        return self._calls[key]
+
 
-    @classmethod
-    def lookup(cls, key: Tuple[Typecode, Device]) -> Callable:
-        return Dispatcher._calls[key]
+Dispatcher: _Dispatcher[Tuple[Typecode, Device]] = _Dispatcher()