如何构造实现自引用泛型Framework trait的Frame枚举实例？

我是Rust新手，目前陷入困境。我定义了枚举Frame，它实现了包含自引用泛型T和关联类型C的Framework trait，代码除测试函数it_works中的构造行外均可正常编译，但我不知道如何构造Frame的新实例，恳请帮助，也欢迎指出设计问题。

原始代码：

use std::collections::HashMap;
use std::sync::Arc;

type Error = "String";

pub enum Value<T> {
    Boolean(bool),
    String("String"),
    Object(Arc<dyn Object<T>>),
    Null,
}

pub type R = Result<(), Error>;

pub type Rv<T> = Result<Arc<Value<T>>, Error>;

pub trait Object<T: Framework> {
    fn name(&self) -> &str;
    fn get(&self, m: &mut T, n: &str) -> Rv<T>;
}

pub trait Framework<T = Self> {
    type C: Clone;
    fn context(&self) -> Option<Self::C>;
    fn process(&mut self, input: Arc<Value<T>>) -> Rv<T>;
}

pub struct FrameBase<T, C: Clone> {
    ctx: Option<C>,
    consts: HashMap<usize, Arc<Value<T>>>,
}

impl<T: Framework, C: Clone> FrameBase<T, C> {
    pub fn new() -> Self {
        Self {
            ctx: None,
            consts: HashMap::<usize, Arc<Value<T>>>::new(),
        }
    }
}

pub enum Frame<T: Framework, C: Clone> {
    Overlay(Box<Frame<T, C>>, FrameBase<T, C>),
    Base(FrameBase<T, C>),
}

impl<T: Framework, C: Clone> Frame<T, C> {
    pub fn new_base(ctx: C) -> Self {
        let base = FrameBase::<T, C> {
            ctx: Some(ctx),
            consts: HashMap::<usize, Arc<Value<T>>>::new(),
        };
        Self::Base(base)
    }
}

impl<T: Framework, C: Clone> Framework for Frame<T, C> {
    type C = C;

    fn context(&self) -> Option<Self::C> {
        match self {
            Self::Overlay(_, base) => match &base.ctx {
                Some(x) => Some(x.clone()),
                None => None,
            },
            Self::Base(base) => match &base.ctx {
                Some(x) => Some(x.clone()),
                None => None,
            },
        }
    }
    fn process(&mut self, _input: Arc<Value<Frame<T, C>>>) -> Rv<Frame<T, C>> {
        let null = Value::Null;
        Ok(Arc::new(null))
    }
}

#[cfg(test)]
mod tests {
    // use std::sync::Arc;
    use super::{Frame, FrameBase, Framework, Value};


    #[test]
    fn it_works() {
        
        // HERE!
        // TODO: How to construct a new instance of Frame?
        let frame = Frame::<, isize>::new_base(0);
        
    }
}

更新：感谢提示，查阅文档后发现，若在 crate 中启用associated_type_defaults特性，可实现自引用。修改后的代码如下：

trait Framework {
    type T = Arc<Self>;
    type C: Clone;
    type S: Storage<Value<Self::T>>;
    fn context(&self) -> Option<Self::C>;
    fn process(&self, store: &mut Self::S, input: Arc<Value<Self::T>>) -> Rv<Self::T>;
}

修改后的代码现已可正常运行。

内容的提问来源于stack exchange，提问作者Yun Luo