215. iNES ROM 数据类

添加

第 215 / 356 · tests/chapter_02_rom_loading/test_215_ines_rom_dataclass.py

添加 emulator/cartridge/ines.py::INesRom。

此步骤存在的原因

这个不可变的解析结果将解释后的文件头与提取出的程序、图形部分放在一起，使得 parse_ines_rom 不必返回零散的值。它建立在第 213-214 课的文件头模型和解析器之上。

在 parse_ines_header 之后的建议实现：

@dataclass(frozen=True)
class INesRom:
    header: INesHeader
    prg_rom: bytes
    chr_rom: bytes

不变量：字段顺序为 header、prg_rom、chr_rom；两个负载都是 bytes 类型；并且该数据类是冻结的，因为它描述的是文件内容。不要将这个格式层面的结果与面向模拟器的 Cartridge 混淆。

此步骤范围之外

1. Lesson 216 calculates offsets, skips trainers, and validates payload size.
2. Lesson 217 introduces the emulator-facing `Cartridge`.
3. Lessons 218-219 implement mapper address translation.

运行本课

uv run pytest tests/chapter_02_rom_loading/test_215_ines_rom_dataclass.py -v

示例实现

此步骤存在的原因

@dataclass(frozen=True)
class INesRom:
    header: INesHeader
    prg_rom: bytes
    chr_rom: bytes

查看测试代码test_215_ines_rom_dataclass.py

import dataclasses
import importlib


def test_ines_rom_class_exists_and_is_frozen_dataclass():
    """
    Objective:
    Create INesRom as a frozen dataclass.

    Why frozen:
    Parsed ROM sections are facts extracted from the file. They should not be
    mutated by the parser result object.
    """
    ines = importlib.import_module("emulator.cartridge.ines")

    assert hasattr(ines, "INesRom")
    assert dataclasses.is_dataclass(ines.INesRom)
    assert ines.INesRom.__dataclass_params__.frozen is True


def test_ines_rom_has_required_fields_in_order():
    """Objective: INesRom stores header, PRG ROM, and CHR ROM."""
    ines = importlib.import_module("emulator.cartridge.ines")

    assert list(ines.INesRom.__dataclass_fields__) == [
        "header",
        "prg_rom",
        "chr_rom",
    ]


def test_ines_rom_can_store_header_prg_and_chr_bytes():
    """
    Objective:
    INesRom should group parsed metadata with extracted ROM byte sections.
    """
    ines = importlib.import_module("emulator.cartridge.ines")
    header = ines.INesHeader(1, 1, 0, False, 0x00, 0x00)

    rom = ines.INesRom(
        header=header,
        prg_rom=bytes([0xA9, 0x42]),
        chr_rom=bytes([0x00, 0x01]),
    )

    assert rom.header is header
    assert rom.prg_rom == bytes([0xA9, 0x42])
    assert rom.chr_rom == bytes([0x00, 0x01])

测试函数 (3)

test_ines_rom_class_exists_and_is_frozen_dataclass
test_ines_rom_has_required_fields_in_order
test_ines_rom_can_store_header_prg_and_chr_bytes