如何移动Vec< Box< dyn Trait>>进入Vec Rc RefCell dyn Trait>. [英] How to move a Vec<Box<dyn Trait>> Into Vec<Rc<RefCell<dyn Trait>>>

问题描述

我有 Vec< Box< dyn Trait>> 作为输入，我想将其元素存储在 Vec< Vc< Rc< RefCell< dyn Trait>>>中..最好的方法是什么?

I have a Vec<Box<dyn Trait>> as input, and I want to store its elements in a Vec<Rc<RefCell<dyn Trait>>>. What is the best way to do it?

我尝试过:

use std::cell::RefCell;
use std::rc::Rc;

trait Trait {}

fn main() {
    let mut source: Vec<Box<dyn Trait>> = Vec::new();
    let mut dest: Vec<Rc<RefCell<dyn Trait>>> = Vec::new();

    for s in source {
        let d = Rc::new(RefCell::new(s.as_ref()));
        dest.push(d);
    }
}

但是我得到了错误:

error[E0277]: the trait bound `&dyn Trait: Trait` is not satisfied
  --> src/main.rs:12:19
   |
12 |         dest.push(d);
   |                   ^ the trait `Trait` is not implemented for `&dyn Trait`
   |
   = note: required for the cast to the object type `dyn Trait`

实际上有可能还是我需要更改输入类型?

Is it actually possible or am I required to change the input type?

推荐答案

如果您控制 Trait ，一种选择是简单地通过 Box< dyn Trait> 实现它推迟到内部实现:

If you control Trait, one option is to simply implement it for Box<dyn Trait> by deferring to the inner implementation:

// We could implement Trait only for Box<dyn Trait>, but usually what you want
// is to implement it for all Boxes of things that are Trait instead
impl<T: ?Sized + Trait> Trait for Box<T> {}

fn pushes(dest: &mut Vec<Rc<RefCell<dyn Trait>>>, source: Vec<Box<dyn Trait>>) {
    for s in source {
        dest.push(Rc::new(RefCell::new(s)));
    }
}

请注意，这会将已经 Box 的对象包装在第二个指针( Rc )的后面，因此，如果您在表演中使用 dest 敏感算法，则必须将其取消引用两次，而不是一次.如果您能够重组代码以接受 Box< T:Trait> ，则可以通过将 T 从 Box移出来消除双重间接.并放入 RefCell .

Be aware this wraps the already-Boxed object behind a second pointer (Rc) so if you are using dest in a performance-sensitive algorithm it will have to dereference it twice rather than once. If you are able to restructure the code so you can accept Box<T: Trait>, you could eliminate the double indirection by moving the T out of the Box and into a RefCell.

• 为什么除非使用临时变量，否则为什么不能插入dyn Trait的Vec?
• 如何通过Rc< RefCell< Box< MyStruct>>>到接受Rc< RefCell< Box< dyn MyTrait>>>>?a的函数(类似的情况，可以消除双向间接访问)
• 未实现大小调整"是什么?(解释为什么上面的示例中需要?Sized )

• Why can't I push into a Vec of dyn Trait unless I use a temporary variable?
• How do I pass Rc<RefCell<Box<MyStruct>>> to a function accepting Rc<RefCell<Box<dyn MyTrait>>>? (a similar case where the double indirection could be eliminated)
• What does "Sized is not implemented" mean? (explains why ?Sized is needed in the above example)

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