我应该使用枚举还是盒装特征对象来模拟多态性? [英] Should I use enums or boxed trait objects to emulate polymorphism?

问题描述

使用枚举Axes来限定Coordinate和Quaternion:

#[derive(Clone)]
pub enum Axes {
    Coordinate {
        x: f64,
        y: f64,
        z: f64,
        reserve: Vec<f64>,
    },
    Quaternion {
        x: f64,
        y: f64,
        z: f64,
    },
}

impl Axes {
    pub fn shift(&mut self, Sample: &Axes) -> () {
        let Dup: Axes = self.clone();
        match Dup {
            Axes::Coordinate { x, y, z, reserve } => match &Sample {
                Axes::Coordinate { x, y, z, reserve } => {
                    *self = Axes::Coordinate {
                        x: *x,
                        y: *y,
                        z: *z,
                        reserve: reserve.to_vec(),
                    };
                }
                _ => panic!(),
            },
            Axes::Quaternion { x, y, z } => match &Sample {
                Axes::Quaternion { x, y, z } => {
                    *self = Axes::Quaternion {
                        x: *x,
                        y: *y,
                        z: *z,
                    };
                }
                _ => panic!(),
            },
        }
    }
}

使用 trait Axes 链接 Coordinate 和 Quaternion 结构:

Using the trait Axes to link the Coordinate and Quaternion structs:

pub trait Axes {
    fn shift(&mut self, Sample: &Axes) -> ();
    fn fold(&mut self, Sample: &Axes) -> ();
}

pub struct Coordinate {
    pub x: f64,
    pub y: f64,
    pub z: f64,
    pub reserve: Vec<f64>,
}

pub struct Quaternion {
    pub x: f64,
    pub y: f64,
    pub z: f64,
}

impl Axes for Coordinate {
    fn shift(&mut self, Sample: &Axes) -> () {}
    fn fold(&mut self, Sample: &Axes) -> () {}
}

impl Axes for Quaternion {
    fn shift(&mut self, Sample: &Axes) -> () {}
    fn fold(&mut self, Sample: &Axes) -> () {}
}

在这种情况下，结构上实现的特征是否更易于访问和更有效?我对使用哪个以及在什么情况下感到困惑.

Is a trait implemented on structs more accessible and more efficient in this case? I am confused of which to use and in what cases.

推荐答案

根据您的情况使用特征和枚举的一大区别是它们的可扩展性.如果您将 Axes 设为枚举，则这两个选项将被硬编码到类型中.如果要添加第三种形式的轴，则必须修改类型本身，这可能涉及使用 Axes 对代码进行大量修改(例如，在 Axes 可能需要更改).另一方面，如果您将 Axes 设为 trait，您可以通过定义一个新类型并编写适当的实现来添加其他类型的轴，而根本不需要修改现有代码.这甚至可以从图书馆外部完成，例如由用户.

One of the big differences between using traits and enums for your situation is their extensibility. If you make Axes an enum, then the two options are hardcoded into the type. If you want to add some third form of axis, you'll have to modify the type itself, which will probably involve a lot of modifications to the code with uses Axes (e.g. anywhere you match on an Axes will probably need to be changed). On the other hand, if you make Axes a trait, you can add other types of axes by just defining a new type and writing an appropriate implementation, without modifying existing code at all. This could even be done from outside of the library, e.g. by a user.

要考虑的另一件重要事情是您需要对结构内部进行多少访问.使用枚举，您可以完全访问存储在结构中的所有数据.如果您想编写一个可以使用特征同时对 Coordinate 和 Quaternion 进行操作的函数，那么您将能够执行的唯一操作是 Axes 特征(在本例中为 Shift 和 Fold).例如，给出您给出的 Axes 的实现，您将无法通过 Axes 简单地检索 (X,Y,Z) 元组 接口.如果您需要在某个时候这样做，则必须添加一个新方法.

The other important thing to consider is how much access you need to the internals of the structs. With an enum, you get full access to all the data stored within the struct. If you want to write a function which can operate on both Coordinate and Quaternion using a trait, then the only operations you will be able to perform are those described in the Axes trait (in this case Shift and Fold). For instance, giving the implementation of Axes you gave, there would be no way for you to simply retrieve the (X,Y,Z) tuple via the Axes interface. If you needed to do that at some point, you would have to add a new method.

如果不了解您计划如何使用这些类型的更多信息，很难确定哪些选项是更好的选择，但如果是我，我可能会使用枚举.归根结底，这主要取决于偏好，但希望这能让您对做出决定时需要考虑的事项有所了解.

Without knowing more about how you plan to use these types it's difficult to say for sure which of these options is the better choice, but if it were me I would probably use an enum. Ultimately, it comes down largely to preference, but hopefully this will give you some idea of the sorts of things to be thinking about when making your decision.

这篇关于我应该使用枚举还是盒装特征对象来模拟多态性?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！