Document dataclass field should not be reused

Documentation

The current implementation of dataclass modifies a field in place. Thereby, the following code will modify f:

from dataclasses import dataclass, field

f = field(kw_only=True)

@dataclass
class A:
    x: int = f
    y: int = f

print(f) # now f.name is filled
# furthermore, A is broken (or does not behave if we used two different field instance)

It can create issues when we have multiple fields that have the same spec and we reuse the same Field instance to set the same metadata to all of them. A class is created but it's garbage.

IMHO, in the docs, we should warn the user to NOT share any Field instance.

Linked PRs

• gh-145373
• gh-145387

首先查閱 dataclass 和 Field 文件以及連結的 PR gh-145373 和 gh-145387。新增明確警告，不要在 dataclass 欄位之間重複使用同一個 Field 實例；當文件中的指引處理了由此產生的變異和異常的類別行為時，將 issue 中的範例視為完整。