我可以使用附加值扩充枚举吗？ [英] Can I extend an enum with additional values?

问题描述

如果我有一个具有一组值的枚举，有没有办法创建一个具有相同变体的第二个枚举呢？

If I have an enum with a set of values, is there a way I could create a second enum with the same variants plus some more?

// From this
enum Base {
    Alpha,
    Beta(usize),
}

// To this, but without copy & paste
enum Extended {
    Alpha,
    Beta(usize),
    Gamma,
}

推荐答案

一个枚举不能被直接扩展，但你使用与struct相同的组合技巧（即，使用一个struct，一个字段存储'parent'的一个实例。

An enum can't be directly extended, but you use the same composition trick one would use with structs (that is, with a struct, one would have a field storing an instance of the 'parent').

enum Extended {
    Base(Base),
    Gamma
}

如果您想单独处理每个案例，然后使用它像

If you wish to handle each case individually, this is then used like

match some_extended {
    Base(Alpha) => ...,
    Base(Beta(x)) => ...,
    Gamma => ...
}

但您也可以从父母

match some_extended {
    Base(base) => base.do_something(),
    Gamma => ...,
}

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