Extended MagicFilter with aiogram-specific operation (#759)

* Extend MagicFilter with aiogram-specific operation

* Added tests

* Added changes annotation and update docs

aiogram/__init__.py

@@ -1,11 +1,10 @@
-from magic_filter import MagicFilter
-
 from .client import session
 from .client.bot import Bot
 from .dispatcher import filters, handler
 from .dispatcher.dispatcher import Dispatcher
 from .dispatcher.middlewares.base import BaseMiddleware
 from .dispatcher.router import Router
+from .utils.magic_filter import MagicFilter
 from .utils.text_decorations import html_decoration as _html_decoration
 from .utils.text_decorations import markdown_decoration as _markdown_decoration
 

aiogram/utils/magic_filter.py

@@ -0,0 +1,21 @@
+from typing import Any
+
+from magic_filter import MagicFilter as _MagicFilter
+from magic_filter import MagicT as _MagicT
+from magic_filter.operations import BaseOperation
+
+
+class AsFilterResultOperation(BaseOperation):
+    __slots__ = ("name",)
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+
+    def resolve(self, value: Any, initial_value: Any) -> Any:
+        if value:
+            return {self.name: value}
+
+
+class MagicFilter(_MagicFilter):
+    def as_(self: _MagicT, name: str) -> _MagicT:
+        return self._extend(AsFilterResultOperation(name=name))