如何在成员方法关闭中使用struct self [英] How to use struct self in member method closure
本文介绍了如何在成员方法关闭中使用struct self的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
如何在闭包中调用方法? get_access_token方法可以基于self.get_base_url()设置新的访问令牌:
How can I call a method in closure? get_access_token method can set new access token based on 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:
2015年锈蚀
error[E0500]: closure requires unique access to `self` but `self.access_token` is already borrowed
--> src/main.rs:26:33
|
25 | self.access_token
| ----------------- borrow occurs here
26 | .get_or_insert_with(|| fetch_access_token(self.get_base_url()))
| ^^ ---- borrow occurs due to use of `self` in closure
| |
| closure construction occurs here
27 | }
| - borrow ends here
2018年锈蚀
error[E0501]: cannot borrow `self.access_token` as mutable because previous closure requires unique access
--> src/main.rs:25:9
|
25 | / self.access_token
26 | | .get_or_insert_with(|| fetch_access_token(self.get_base_url()))
| |______________------------------_--____________________----________________^ second borrow occurs here
| | | |
| | | first borrow occurs due to use of `self` in closure
| | closure construction occurs here
| first borrow later used by call
error[E0500]: closure requires unique access to `self` but it is already borrowed
--> src/main.rs:26:33
|
24 | pub fn get_access_token(&mut self) -> &String {
| - let's call the lifetime of this reference `'1`
25 | self.access_token
| -----------------
| |
| _________borrow occurs here
| |
26 | | .get_or_insert_with(|| fetch_access_token(self.get_base_url()))
| |_________________________________^^____________________----________________- returning this value requires that `self.access_token` is borrowed for `'1`
| | |
| | second borrow occurs due to use of `self` in closure
| closure construction occurs here
推荐答案
将数据和方法拆分为较小的组件，然后您可以对self上的各个组件进行不相交的借用:
Split your data and methods into smaller components, then you can take disjoint borrows to various components on self:
fn fetch_access_token(_base_url: &str) -> String { String::new() }
fn get_env_url() -> String { String::new() }
#[derive(Default)]
struct BaseUrl(Option<String>);
impl BaseUrl {
fn get(&mut self) -> &str {
self.0.get_or_insert_with(|| get_env_url())
}
}
#[derive(Default)]
struct App {
base_url: BaseUrl,
access_token: Option<String>,
}
impl App {
fn new() -> App {
App::default()
}
fn get_access_token(&mut self) -> &str {
let base_url = &mut self.base_url;
self.access_token
.get_or_insert_with(|| fetch_access_token(base_url.get()))
}
}
fn main() {}
您可以进一步做这两个值:
You can go further and do this for both values:
fn fetch_access_token(_base_url: &str) -> String { String::new() }
fn get_env_url() -> String { String::new() }
#[derive(Default)]
struct BaseUrl(Option<String>);
impl BaseUrl {
fn get(&mut self) -> &str {
self.0.get_or_insert_with(|| get_env_url())
}
}
#[derive(Default)]
struct AccessToken(Option<String>);
impl AccessToken {
fn get(&mut self, base_url: &str) -> &str {
self.0.get_or_insert_with(|| fetch_access_token(base_url))
}
}
#[derive(Default)]
struct App {
base_url: BaseUrl,
access_token: AccessToken,
}
impl App {
fn new() -> App {
App::default()
}
fn get_access_token(&mut self) -> &str {
let base_url = self.base_url.get();
self.access_token.get(base_url)
}
}
fn main() {}
让您看到可以抽象出常见功能:
Which lets you see that you can abstract out common functionality:
fn fetch_access_token(_base_url: &str) -> String { String::new() }
fn get_env_url() -> String { String::new() }
#[derive(Default)]
struct StringCache(Option<String>);
impl StringCache {
fn get<F>(&mut self, f: F) -> &str
where
F: FnOnce() -> String,
{
self.0.get_or_insert_with(f)
}
}
#[derive(Default)]
struct App {
base_url: StringCache,
access_token: StringCache,
}
impl App {
fn new() -> App {
App::default()
}
fn get_access_token(&mut self) -> &str {
let base_url = self.base_url.get(get_env_url);
self.access_token.get(|| fetch_access_token(base_url))
}
}
fn main() {}
然后您意识到抽象可以通用:
And then you realize the abstraction can be made generic:
fn fetch_access_token(_base_url: &str) -> String { String::new() }
fn get_env_url() -> String { String::new() }
#[derive(Default)]
struct Cache<T>(Option<T>);
impl<T> Cache<T> {
fn get<F>(&mut self, f: F) -> &T
where
F: FnOnce() -> T,
{
self.0.get_or_insert_with(f)
}
}
#[derive(Default)]
struct App {
base_url: Cache<String>,
access_token: Cache<String>,
}
impl App {
fn new() -> App {
App::default()
}
fn get_access_token(&mut self) -> &str {
let base_url = self.base_url.get(get_env_url);
self.access_token.get(|| fetch_access_token(base_url))
}
}
fn main() {}
另请参阅:
- Borrowing references to attributes in a struct
- Why is it discouraged to accept a reference to a String (&String), Vec (&Vec) or Box (&Box) as a function argument?
- The Rust Programming Language chapter on closures, which creates this caching struct as part of the exercises.
这篇关于如何在成员方法关闭中使用struct self的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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