feat: add generic in SingleInstanceMetaClass

Signed-off-by: csy1204 <josang1204@gmail.com>

pymilvus/orm/connections.py

@@ -15,7 +15,7 @@
 import pathlib
 import threading
 import time
-from typing import Callable, Tuple, Union
+from typing import Callable, Generic, Tuple, TypeVar, Union
 from urllib import parse
 
 from pymilvus.client.check import is_legal_address, is_legal_host, is_legal_port
@@ -31,6 +31,8 @@
 
 VIRTUAL_PORT = 443
 
+T = TypeVar("T")
+
 
 def synchronized(func: Callable):
     """
@@ -45,13 +47,13 @@ def lock_func(*args, **kwargs):
     return lock_func
 
 
-class SingleInstanceMetaClass(type):
+class SingleInstanceMetaClass(Generic[T]):
     instance = None
 
     def __init__(cls, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
 
-    def __call__(cls, *args, **kwargs):
+    def __call__(cls, *args, **kwargs) -> T:
         if cls.instance:
             return cls.instance
         cls.instance = cls.__new__(cls)