英文:
How can I add another enum variant in Rust without breaking library users?
问题
在我的Rust库中的某处定义了以下枚举类型：
#[derive(Debug)]
pub enum Color {
Red,
Green,
Blue,
}
当我向该枚举添加第四个变体Color::Yellow时，是否被视为破坏性更改？如果它被视为破坏性更改（我猜是因为match语句），是否有一种方法可以向API用户指示该类型可能在将来扩展？
英文:
Assume the following enumeration type is defined somewhere in my Rust library:
#[derive(Debug)]
pub enum Color {
Red,
Green,
Blue,
}
Is it considered a breaking change when I add a fourth variant Color::Yellow to the enum? If it is a breaking change (I guess so because of the match statement), is there a way to indicate to API users that this type might be extended in the future?
答案1
得分: 3
是的，添加一个枚举变体被视为一个破坏性的变更。在Rust RFC 1105 - API演进中可以阅读更多相关信息 这里。
你可以在你的枚举上添加#[non_exhaustive]属性，以警告你的用户，你可能在未来扩展你的枚举以包含更多的变体，这样添加一个新的变体就不会被视为破坏性变更：
#[non_exhaustive]
#[derive(Debug)]
pub enum Color {
Red,
Green,
Blue,
}
这会禁止导入你的枚举的项目进行非穷尽匹配。例如：
match color {
Color::Red => (),
Color::Green => (),
Color::Blue => (),
}
会抛出错误，而
match color {
Color::Red => (),
Color::Green => (),
Color::Blue => (),
_ => (),
}
则不会。
英文:
Yes, adding an enum variant is considered a breaking change. Read more about it in the Rust RFC 1105 - API evolution here.
You can add the #[non_exhaustive] attribute to your enum to warn your users that you may extend your enum with further variants in the future, so adding a new variant won't be considered a breaking change:
#[non_exhaustive]
#[derive(Debug)]
pub enum Color {
Red,
Green,
Blue,
}
This disallows projects that import your enum to non-exhaustively match it. I.e.:
match color {
Color::Red => (),
Color::Green => (),
Color::Blue => (),
}
throws an error, while
match color {
Color::Red => (),
Color::Green => (),
Color::Blue => (),
_ => (),
}
won't.
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