相关疑难解决方法(0)

如何在闭包中调用方法？get_access_token方法可以基于以下内容设置新的访问令牌self.get_base_url()：

fn fetch_access_token(_base_url: &String) -> String {
    String::new()
}

fn get_env_url() -> String {
    String::new()
}

pub struct App {
    pub base_url: Option<String>,
    pub access_token: Option<String>,
}

impl App {
    pub fn new() -> App {
        App {
            base_url: None,
            access_token: None,
        }
    }
    pub fn get_base_url(&mut self) -> &String {
        self.base_url.get_or_insert_with(|| get_env_url())
    }
    pub fn get_access_token(&mut self) -> &String {
        self.access_token
            .get_or_insert_with(|| fetch_access_token(self.get_base_url()))
    }
}

fn main() {}

错误：

锈2015

fn fetch_access_token(_base_url: &String) -> String …

我试图实现自己的模拟find_or_insert方法,如下所示:

use std::collections::HashMap;

pub struct SomeManager {
    next: i32,
    types: HashMap<i32, i32>,
}

impl SomeManager {
    pub fn get_type<'a>(&'a mut self, k: i32) -> &'a i32 {
        match self.types.get(&k) {
            Some(ref x) => return *x,
            None => {
                self.types.insert(k, self.next);
                self.next += 1;
                return self.types.get(&k).unwrap();
            }
        }
    }
}

fn main() {}

错误:

error[E0502]: cannot borrow `self.types` as mutable because it is also borrowed as immutable
  --> src/main.rs:13:17
   |
10 |         match self.types.get(&k) {
   |               ---------- immutable borrow …