How to handle “cannot infer an appropriate lifetime for autoref due to conflicting requirements”

问题

I have this method from ExchangeInfo struct that returns a RwLockReadGuardRef from owning_ref crate:

pub fn get_pair<'a, 'me: 'a>(
    &'me self,
    name: &str,
) -> RwLockReadGuardRef<'a, TradePairHashMap, Arc<RwLock<TradePair>>> {
    RwLockReadGuardRef::new(self.pairs.read().unwrap()).map(|pairs| pairs.get(name).unwrap())
}

I'm trying to call it here:

pub async fn get_pair<'a>(
    name: &str,
    exchange_info: &'a ExchangeInfo,
    retrieval: &dyn ExchangeInfoRetrieval,
    refresh: bool,
) -> Result<OwningRef<&'a ExchangeInfo, RwLockReadGuard<'a, TradePair>>> {
    if refresh {
        if let Err(err) = exchange_info.refresh(retrieval).await {
            return Err(err);
        }
    }

    Ok(OwningRef::new(exchange_info).map(|e| &e.get_pair(name).read().unwrap()))
}

Unfortunately, I get the following error:

error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
  --> shared/src/exchange_info.rs:25:49
   |
25 |     Ok(OwningRef::new(exchange_info).map(|e| &e.get_pair(name).read().unwrap()))
   |                                                 ^^^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #2 defined on the body at 25:42...
  --> shared/src/exchange_info.rs:25:42
   |
25 |     Ok(OwningRef::new(exchange_info).map(|e| &e.get_pair(name).read().unwrap()))
   |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...so that reference does not outlive borrowed content
  --> shared/src/exchange_info.rs:25:47
   |
25 |     Ok(OwningRef::new(exchange_info).map(|e| &e.get_pair(name).read().unwrap()))
   |                                               ^
note: but, the lifetime must be valid for the lifetime `'a` as defined on the function body at 13:23...
  --> shared/src/exchange_info.rs:13:23
   |
13 | pub async fn get_pair<'a>(
   |                       ^^
note: ...so that the expression is assignable
  --> shared/src/exchange_info.rs:25:5
   |
25 |     Ok(OwningRef::new(exchange_info).map(|e| &e.get_pair(name).read().unwrap()))
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: expected `std::result::Result<owning_ref::OwningRef<&'a exchange_info::ExchangeInfo, std::sync::RwLockReadGuard<'a, _>>, _>`
              found `std::result::Result<owning_ref::OwningRef<&exchange_info::ExchangeInfo, std::sync::RwLockReadGuard<'_, _>>, _>`

How can I fix this ?

There is the complete playground

Thanks for your answers :)

来源：https://stackoverflow.com/questions/63523566/how-to-handle-cannot-infer-an-appropriate-lifetime-for-autoref-due-to-conflicti

标签

rust

reference

lifetime