rust - 如何调用具有泛型类型的结构的关联函数？

Question

我试图创建一个Link trait 和一个结构SinglLink，它具有实现Link 的泛型类型，但是当我调用相关函数时的结构，我得到一个错误。我应该使用像 vec! 这样的宏吗？

mod Link {
    use std::cell::RefCell;
    use std::collections::VecDeque;
    use std::fmt::Debug;
    use std::rc::Rc;

    trait Link {
        type Node;
        type Value;
        fn new(data: &mut VecDeque<Self::Value>) -> Self;
    }

    #[derive(Debug)]
    pub struct Node<T> {
        pub value: T,
        pub next: RefCell<Option<Rc<Node<T>>>>,
    }

    #[derive(Debug)]
    pub struct SinglLink<T> {
        pub header: RefCell<Option<Rc<Node<T>>>>,
        pub len: i32,
    }

    impl<T: Copy> Link for SinglLink<T> {
        type Node = Node<T>;
        type Value = T;
        fn new(data: &mut VecDeque<Self::Value>) -> Self {
            SinglLink {
                header: RefCell::new(None),
                len: 0,
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::Link::SinglLink;
    use super::*;
    use std::cell::RefCell;
    use std::collections::VecDeque;

    #[test]
    fn it_works() {
        let mut data: VecDeque<i32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
        let single: SinglLink<i32> = SinglLink::new(&mut data);
    }
}

错误信息:

error[E0599]: no function or associated item named `new` found for type `Link::SinglLink<_>` in the current scope
  --> src/lib.rs:47:49
   |
20 |     pub struct SinglLink<T> {
   |     ----------------------- function or associated item `new` not found for this
...
47 |         let single: SinglLink<i32> = SinglLink::new(&mut data);
   |                                                 ^^^ function or associated item not found in `Link::SinglLink<_>`
   |
   = help: items from traits can only be used if the trait is implemented and in scope
   = note: the following trait defines an item `new`, perhaps you need to implement it:
           candidate #1: `Link::Link`

Answer 1

这里有两个小错误，使错误消息不是很有用。

1. 您忘记了 trait Link 上的 pub，因此在 Link 模块之外完全无法访问它。例如pub trait Link {/* ... */}

2. 您需要在 tests 模块中使用 Link 特性，以便它的方法在那里可用。 (添加 pub 后，编译器错误会很好地告诉您)。例如使用 super::Link::Link;

这是您的代码的工作版本:

mod Link {
    use std::cell::RefCell;
    use std::collections::VecDeque;
    use std::fmt::Debug;
    use std::rc::Rc;
    pub trait Link {
        type Node;
        type Value;
        fn new(data: &mut VecDeque<Self::Value>) -> Self;
    }

    #[derive(Debug)]
    pub struct Node<T> {
        pub value: T,
        pub next: RefCell<Option<Rc<Node<T>>>>,
    }

    #[derive(Debug)]
    pub struct SinglLink<T> {
        pub header: RefCell<Option<Rc<Node<T>>>>,
        pub len: i32,
    }

    impl<T: Copy> Link for SinglLink<T> {
        type Node = Node<T>;
        type Value = T;
        fn new(data: &mut VecDeque<Self::Value>) -> Self {
            SinglLink {
                header: RefCell::new(None),
                len: 0,
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::Link::SinglLink;
    use super::Link::Link;
    use super::*;
    use std::cell::RefCell;
    use std::collections::VecDeque;

    #[test]
    fn it_works() {
        let mut data: VecDeque<i32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
        let single: SinglLink<i32> = SinglLink::new(&mut data);
    }
}

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