我刚刚学习Rust，在选项中向上转换trait ref时遇到了一些问题。我想将其作为ref传递以减少开销。
其基本思想如下：我有些东西（children）在代码中的其他地方定义，它们是ChildT类型。我需要master能够访问它们的属性并操作它们。还有对象，也需要访问孩子-无论是直接访问还是通过master.get_child。当来自C++时，我想在结构体中存储一个指针。这样可以避免复制开销，并且引用沿着所有想要访问各自子对象的对象保持不变
当实现可变性时，它变得更加复杂，我试图用这种方式克服它：

#![allow(unused)]

use num_traits::Num;
use std::{any::Any, rc::Rc};

pub trait AsBase{

    fn as_base(&self) -> &dyn BaseT;
}

impl <T: BaseT + Sized> AsBase for T{
    fn as_base(&self) -> &dyn BaseT{
        self
    }

}

trait BaseT: AsBase{
    fn get_child(&self) -> Option<Rc<&dyn BaseT>>;
    fn get_child_mut(&mut self) -> Option<&mut Rc<&dyn BaseT>>;
}

trait ChildT: BaseT{
    fn child_t_fn(&self);
}

struct C1{
    child: Option<Rc<dyn ChildT>>,
}

impl BaseT for C1{
    fn get_child(&self) -> Option<Rc<&dyn BaseT>> {
        match &self.child{
            Some(x) => return Some(Rc::new(x.as_base()) ),
            None => return None
        }
    }
    fn get_child_mut(&mut self) -> Option<&mut Rc<&dyn BaseT>> {
        match &self.child{
            Some(x) => return Some(&mut Rc::new(x.as_base()) ),
            None => return None
        }
    }
}

impl ChildT for C1{
    fn child_t_fn(&self) {
        
    }
}

// same as C2 code-wise, for the sake of simplicity
struct C2{
    child: Option<Rc<dyn ChildT>>,
}

impl BaseT for C2{
    fn get_child(&self) -> Option<Rc<&dyn BaseT>> {
        match &self.child{
            Some(x) => return Some(Rc::new(x.as_base()) ),
            None => return None
        }
    }
    fn get_child_mut(&mut self) -> Option<&mut Rc<&dyn BaseT>> {
        match &self.child{
            Some(x) => return Some(&mut Rc::new(x.as_base()) ), // <- cannot pass temp. variable
            None => return None
        }
    }
}
impl ChildT for C2{
    fn child_t_fn(&self) {
        
    }
}

// receive two structs, change one child
fn test(c1: &mut Rc<&dyn ChildT>, c2: &mut Rc<&dyn ChildT>){
    let old_child = c2.get_child_mut();

    let mut new_val: Rc<&dyn BaseT> = Rc::new(c1.as_base());
    old_child = Some(new_val); // <- doesnt work. cannot make it mutable (I think because it is temp and would pass to another struct losing scope. how to overcome that?)
}

fn main(){
    // Example use of the upper code
    let c1 = C1{
            child: None
        };
    let mut c2 = C2{
        child: Some(Rc::new(c1))
    };
    let mut c3 = C2{
        child: Some(Rc::new(c2))
    };
    let mut c4 = C1{
        child: Some(Rc::new(c3))
    };
    
    // i just skipped the function .as_child(), it is basically the same as to_base
    test(Rc::new(c4.as_child()),Rc::new(c2.as_child()));

}

字符串