rust - 存储具有相同特征和不同输出类型的结构

Question

This question already has answers here:

How can I have a collection of objects that differ by their associated type?

(3个答案)



How do I create a heterogeneous collection of objects?

(1个答案)


在4个月前关闭。




我试图将具有共同特征的不同结构存储在 Vec<Box<dyn ...集合中。
这似乎很困难，因为 impl Trait for Struct具有不同的输出类型。
playground

fn main()
{
    let p = TheirPoint ...
    let l = TheirLine ...
    let vec_shapes: Vec<Box<dyn TheirShadow>> = vec![Box::new(l), Box::new(p)];
}

impl TheirShadow for TheirPoint {
    type Output = (TheirPoint, TheirPoint);
...
}

impl TheirShadow for TheirLine {
    type Output = (TheirPoint, TheirPoint, TheirPoint, TheirPoint);
...
}

pub trait TheirShadow {
    type Output;
...
}

error[E0191]: the value of the associated type `Output` (from trait `TheirShadow`) must be specified
  --> src/main.rs:32:33
   |
32 |     let vec_shapes: Vec<Box<dyn TheirShadow>> = vec![Box::new(l), Box::new(p)];
   |                                 ^^^^^^^^^^^ help: specify the associated type: `TheirShadow<Output = Type>`
...
73 |     type Output;
   |     ------------ `Output` defined here

这可以实现吗，或者像另一个问题答案中那样类似于 The signatures for all methods of all items in a collection must be identical, so that you can use them interchangeably？

最佳答案

由于您不知道Output，因此实际上不能使用返回Output的函数，因为它们的大小都是不同的，而Rust无法知道将返回哪个函数。解决此问题的最简单方法是使用枚举:

enum Shadow {
    Tuple2(TheirPoint, TheirPoint),
    Tuple4(TheirPoint, TheirPoint, TheirPoint, TheirPoint)
}

impl TheirShadow for TheirPoint {
    type Output = Shadow;
    fn cast_shadow(self) -> Self::Output {
        Shadow::Tuple2(some_point, some_other_point)
    }
}

// and so on

您甚至可以消除 Output类型，而只在特征中强制返回 Shadow的返回值。

关于rust - 存储具有相同特征和不同输出类型的结构，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/64916571/

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Answer 1

由于您不知道Output，因此实际上不能使用返回Output的函数，因为它们的大小都是不同的，而Rust无法知道将返回哪个函数。解决此问题的最简单方法是使用枚举:

enum Shadow {
    Tuple2(TheirPoint, TheirPoint),
    Tuple4(TheirPoint, TheirPoint, TheirPoint, TheirPoint)
}

impl TheirShadow for TheirPoint {
    type Output = Shadow;
    fn cast_shadow(self) -> Self::Output {
        Shadow::Tuple2(some_point, some_other_point)
    }
}

// and so on

您甚至可以消除 Output类型，而只在特征中强制返回 Shadow的返回值。