我正在像这样使用 Warp:
#[derive(Default)]
struct State {
topics: HashMap<String, Topic>,
}
struct Topic {
name: String,
description: String,
items: Vec<String>,
}
fn with_state(state: Arc<Mutex<State>>) -> impl Filter<Extract = (Arc<Mutex<State>>,), Error = std::convert::Infallible> + Clone {
warp::any().map(move || state.clone())
}
#[tokio::main]
async fn main() {
let state = Arc::new(Mutex::new(State::default()));
let survey = warp::get()
.and(warp::path!("survey" / String))
.and(warp::path::end())
.and(with_state(state.clone()))
.and_then(|topic: String, state: Arc<Mutex<State>>| async move {
let state = state.lock().unwrap();
let topic = state.topics.get(&topic).ok_or(warp::reject::not_found())?;
let res: Result<Value, Rejection> = Ok(json!({
"name": topic.name,
"items": topic.items.iter().map(AsRef::as_ref).collect::<Value>(),
}));
res
})
...
如果我编译它会给出这个错误:
error[E0283]: type annotations needed for `std::string::String`
--> src/main.rs:210:20
|
210 | .and_then(|topic: String, state: Arc<Mutex<State>>| async move {
| ^^^^^ consider giving this closure parameter a type
|
= note: cannot resolve `std::string::String: std::convert::AsRef<_>`
= note: required by `std::convert::AsRef::as_ref`
这真的很奇怪。这是什么意思consider giving this closure parameter a type
?它不是已经有类型了吗?更奇怪的是,如果我注释掉这一行:
"items": topic.items.iter().map(AsRef::as_ref).collect::<Value>(),
然后它编译!topic
即使该行显然与参数无关。这是怎么回事?