如何构建Rust中向量的HashMap

我是个新手.我试图将一个有向图的邻接列表表示为char{vertex name}到(char，int){vertex name，cost}向量的HashMap.我希望最终的HashMap是不可变的，但我希望构建向量，然后不需要复制它来使其不可变.

My code is below. At the indicated line I get "cannot borrow immutable dereference (dereference is implicit, due to indexing) as mutable". This makes sense, as the Vec<(char,int)> in the map is not mutable. But I'm not sure how to fix it.

有没有办法在Rust 的地方做到这一点？

pub struct Edge {
    to:     char,
    from:   char,
    weight: int
}

pub struct digraph {
    _vertices:  Vec<char>,
    _adj_list:  HashMap<char, Vec<(char,int)> >
}

impl digraph {
    pub fn new(nodes: &Vec<char>, edges: &Vec<Edge> ) -> Option<digraph> {
        let mut tmp_adj_list = HashMap::new();
        for node in (*nodes).iter() {
            tmp_adj_list.insert(*node, Vec::new());
        }
        for edge in (*edges).iter() {
            let Edge{ to: to, from:from, weight:weight } = *edge;
            if  !(*nodes).contains(&to) |  !(*nodes).contains(&from) {
                return None;
            }
            tmp_adj_list[from].push((to,weight))  // *********** error here
        }
        Some(digraph { _vertices: (*nodes).clone(), _adj_list: tmp_adj_list })
    }
}