text: # pylint: disable=missing-class-docstring,missing-function-docstring,missing-module-docstring
  from __future__ import annotations
  
  from dataclasses import dataclass
  from typing import ClassVar
  
  from typing_extensions import Annotated
  
  from configpile import Config, Expander, Param, parsers
  
  
  @dataclass(frozen=True)
  class A(Config):
      a: Annotated[int, Param.store(parsers.int_parser, default_value="2")]
      set_a_to_zero: ClassVar[Expander] = Expander.make("--a", "0")
  
  
  def test_expander() -> None:
      res = A.from_command_line_(args=["--set-a-to-zero"], env={})
      assert isinstance(res, A)
      assert res.a == 0
  