问当关联类型没有大小时，如何避免需要``std：：marker：：size‘？

EN

pub struct XKernel;

pub trait KernelDense {
    fn compute_dense(&self, vectors: &[f32]);
}

impl KernelDense for XKernel {
    fn compute_dense(&self, vectors: &[f32]) {}
}

pub trait KernelCompute<V> {
    fn just_compute_it(&self, vectors: &[V]);
}

impl KernelCompute<f32> for (dyn KernelDense + 'static) {
    fn just_compute_it(&self, v: &[f32]) {
        self.compute_dense(v);
    }
}

pub trait Generalization {
    type V: 'static;

    type OperatorType: KernelCompute<Self::V>;

    fn set_kernel(&self, x: Box<Self::OperatorType>);

    fn compute(&self, v: &[Self::V]);
}

pub struct DenseVariant {
    x: Box<KernelDense>,
}

impl Generalization for DenseVariant {
    type V = f32;
    type OperatorType = KernelDense;

    fn set_kernel(&self, x: Box<KernelDense>) {}

    fn compute(&self, v: &[Self::V]) {
        self.x.compute_dense(v);
    }
}

struct BlackBox<'a, T>
where
    T: Generalization,
{
    computer: T,
    elements: &'a [T::V],
}

impl<'a, T> BlackBox<'a, T>
where
    T: Generalization,
{
    fn runtime_pick_operator_and_compute(&mut self) {
        self.computer.set_kernel(Box::new(XKernel));
        let s = self.elements.as_ref();
        self.computer.compute(s);
    }
}

fn main() {
    // What I eventually want to do:
    // let black_box = BlackBox::<DenseVariant>::new();
    // black_box.runtime_pick_operator_and_compute();
}

error[E0277]: the size for values of type `(dyn KernelDense + 'static)` cannot be known at compilation time
  --> src/main.rs:35:6
   |
35 | impl Generalization for DenseVariant {
   |      ^^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `std::marker::Sized` is not implemented for `(dyn KernelDense + 'static)`
   = note: to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-sized>