Struct Promise

pub struct Promise<T>(/* private fields */);

Available on crate features runtime and component-model and component-model-async only.

Represents the result of a concurrent operation.

This is similar to a std::future::Future except that it represents an operation which requires exclusive access to a store in order to make progress – without monopolizing that store for the lifetime of the operation.

Implementations

impl<T: 'static> Promise<T>

pub fn map<U>( self, fun: impl FnOnce(T) -> U + Send + Sync + 'static, ) -> Promise<U>

Map the result of this Promise from one value to another.

pub async fn get<U: Send>(self, store: impl AsContextMut<Data = U>) -> Result<T>

Convert this Promise to a future which may be awaited for its result.

The returned future will require exclusive use of the store until it completes. If you need to await more than one Promise concurrently, use PromisesUnordered.

pub fn into_future( self, ) -> Pin<Box<dyn Future<Output = T> + Send + Sync + 'static>>

Convert this Promise to a future which may be awaited for its result.

Unlike Self::get, this does not take a store parameter, meaning the returned future will not make progress until and unless the event loop for the store it came from is polled. Thus, this method should only be used from within host functions and not from top-level embedder code.