如何实现枚举及其各自变体的特征? [英] How do I implement a trait for an enum and its respective variants?

问题描述

我正在尝试使用枚举变量来捕获本质上是异构的(具有不同的字段集合)但从协议角度来看属于同一类型"的数据.但是，我不确定如何实现特定于子类型的方法和特征.这是一个最小的示例，说明如何创建数据枚举以及可以使用枚举变量构造函数来指定类型，但是如果我在变量上实现特征，则无法确定调用该函数的方法

I'm trying to use enum variants to capture data which is heterogeneous in nature (has different collections of fields) but which is of the same "type" from a protocol perspective. However, I'm not sure how to implement subtype-specific methods and traits. Here is a minimal example of how I can create an enumeration of Data and I can use enum variant constructors to specify the types, but if I implement a trait on the variant, calling that function is not something I've figured out how to do.

use std::fmt;

enum Data {
    N(NData),
    S(SData),
}

struct NData {
    numeric: u32,
}

impl fmt::Display for NData {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.numeric)
    }
}

struct SData {
    stringy: Vec<String>,
}

fn main() {
    let d_n: Data = Data::N(NData { numeric: 0x0 });
    let n = NData { numeric: 0xff };

    // Fails, fmt::Display not implemented for Data
    println!("{}", d_n);

    // Just fine!
    println!("{}", n);
}

推荐答案

一种可能的解决方案是为变体以及 enum 实现您的特征，您只能在此处看到调用变体的特定实现:

One possible solution could be to implement your trait for the variants as well as for the enum, which as you can see here only calls the specific implementations of the variants:

use std::fmt;

struct NData {
    numeric: u32,
}

impl fmt::Display for NData {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.numeric)
    }
}

struct SData {
    strings: Vec<String>,
}

impl fmt::Display for SData {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{:?}", self.strings)
    }
}

enum Data {
    N(NData),
    S(SData),
}

impl fmt::Display for Data {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Data::N(n_data) => n_data.fmt(f),
            Data::S(s_data) => s_data.fmt(f),
        }
    }
}

fn main() {
    let n = NData { numeric: 0xff };
    let s = SData { strings: vec!["hello".to_string(), "world".to_string()] };

    println!("{}", n);
    println!("{}", s);

    let d_n = Data::N(n);
    let d_s = Data::S(s);

    println!("{}", d_n);
    println!("{}", d_s);
}

这将产生以下输出:

255
["hello", "world"]
255
["hello", "world"]

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