Struct futures_util::stream::Once

source · 
pub struct Once<Fut> { /* private fields */ }
Expand description

A stream which emits single element and then EOF.

Trait Implementations§

source§

impl<Fut: Debug> Debug for Once<Fut>

source§

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

impl<Fut: Future> FusedStream for Once<Fut>

source§

fn is_terminated(&self) -> bool

Returns true if the stream should no longer be polled.
source§

impl<Fut: Future> Stream for Once<Fut>

§

type Item = <Fut as Future>::Output

Values yielded by the stream.
source§

fn poll_next( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll<Option<Self::Item>>

Attempt to pull out the next value of this stream, registering the current task for wakeup if the value is not yet available, and returning None if the stream is exhausted. Read more
source§

fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the stream. Read more
source§

impl<'__pin, Fut> Unpin for Once<Fut>
where __Origin<'__pin, Fut>: Unpin,

Auto Trait Implementations§

§

impl<Fut> Freeze for Once<Fut>
where Fut: Freeze,

§

impl<Fut> RefUnwindSafe for Once<Fut>
where Fut: RefUnwindSafe,

§

impl<Fut> Send for Once<Fut>
where Fut: Send,

§

impl<Fut> Sync for Once<Fut>
where Fut: Sync,

§

impl<Fut> UnwindSafe for Once<Fut>
where Fut: UnwindSafe,

Blanket Implementations§

source§

impl<T> Any for T
where T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T> Borrow<T> for T
where T: ?Sized,

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T, U> Into<U> for T
where U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

source§

impl<T> StreamExt for T
where T: Stream + ?Sized,

source§

fn next(&mut self) -> Next<'_, Self> ⓘ
where Self: Unpin,

Creates a future that resolves to the next item in the stream. Read more
source§

fn into_future(self) -> StreamFuture<Self> ⓘ
where Self: Sized + Unpin,

Converts this stream into a future of (next_item, tail_of_stream). If the stream terminates, then the next item is None. Read more
source§

fn map<T, F>(self, f: F) -> Map<Self, F>
where F: FnMut(Self::Item) -> T, Self: Sized,

Maps this stream’s items to a different type, returning a new stream of the resulting type. Read more
source§

fn enumerate(self) -> Enumerate<Self>
where Self: Sized,

Creates a stream which gives the current iteration count as well as the next value. Read more
source§

fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Filters the values produced by this stream according to the provided asynchronous predicate. Read more
source§

fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = Option<T>>, Self: Sized,

Filters the values produced by this stream while simultaneously mapping them to a different type according to the provided asynchronous closure. Read more
source§

fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>
where F: FnMut(Self::Item) -> Fut, Fut: Future, Self: Sized,

Computes from this stream’s items new items of a different type using an asynchronous closure. Read more
source§

fn collect<C: Default + Extend<Self::Item>>(self) -> Collect<Self, C> ⓘ
where Self: Sized,

Transforms a stream into a collection, returning a future representing the result of that computation. Read more
source§

fn unzip<A, B, FromA, FromB>(self) -> Unzip<Self, FromA, FromB> ⓘ
where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Sized + Stream<Item = (A, B)>,

Converts a stream of pairs into a future, which resolves to pair of containers. Read more
source§

fn concat(self) -> Concat<Self> ⓘ
where Self: Sized, Self::Item: Extend<<<Self as Stream>::Item as IntoIterator>::Item> + IntoIterator + Default,

Concatenate all items of a stream into a single extendable destination, returning a future representing the end result. Read more
source§

fn count(self) -> Count<Self> ⓘ
where Self: Sized,

Drives the stream to completion, counting the number of items. Read more
source§

fn cycle(self) -> Cycle<Self>
where Self: Sized + Clone,

Repeats a stream endlessly. Read more
source§

fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F> ⓘ
where F: FnMut(T, Self::Item) -> Fut, Fut: Future<Output = T>, Self: Sized,

Execute an accumulating asynchronous computation over a stream, collecting all the values into one final result. Read more
source§

fn any<Fut, F>(self, f: F) -> Any<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Execute predicate over asynchronous stream, and return true if any element in stream satisfied a predicate. Read more
source§

fn all<Fut, F>(self, f: F) -> All<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Execute predicate over asynchronous stream, and return true if all element in stream satisfied a predicate. Read more
source§

fn flatten(self) -> Flatten<Self>
where Self::Item: Stream, Self: Sized,

Flattens a stream of streams into just one continuous stream. Read more
source§

fn flatten_unordered( self, limit: impl Into<Option<usize>>, ) -> FlattenUnordered<Self>
where Self::Item: Stream + Unpin, Self: Sized,

Flattens a stream of streams into just one continuous stream. Polls inner streams produced by the base stream concurrently. Read more
source§

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
where F: FnMut(Self::Item) -> U, U: Stream, Self: Sized,

Maps a stream like StreamExt::map but flattens nested Streams. Read more
source§

fn flat_map_unordered<U, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> FlatMapUnordered<Self, U, F>
where U: Stream + Unpin, F: FnMut(Self::Item) -> U, Self: Sized,

Maps a stream like StreamExt::map but flattens nested Streams and polls them concurrently, yielding items in any order, as they made available. Read more
source§

fn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F>
where F: FnMut(&mut S, Self::Item) -> Fut, Fut: Future<Output = Option<B>>, Self: Sized,

Combinator similar to StreamExt::fold that holds internal state and produces a new stream. Read more
source§

fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Skip elements on this stream while the provided asynchronous predicate resolves to true. Read more
source§

fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F>
where F: FnMut(&Self::Item) -> Fut, Fut: Future<Output = bool>, Self: Sized,

Take elements from this stream while the provided asynchronous predicate resolves to true. Read more
source§

fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut>
where Fut: Future, Self: Sized,

Take elements from this stream until the provided future resolves. Read more
source§

fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = ()>, Self: Sized,

Runs this stream to completion, executing the provided asynchronous closure for each element on the stream. Read more
source§

fn for_each_concurrent<Fut, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> ForEachConcurrent<Self, Fut, F> ⓘ
where F: FnMut(Self::Item) -> Fut, Fut: Future<Output = ()>, Self: Sized,

Runs this stream to completion, executing the provided asynchronous closure for each element on the stream concurrently as elements become available. Read more
source§

fn take(self, n: usize) -> Take<Self>
where Self: Sized,

Creates a new stream of at most n items of the underlying stream. Read more
source§

fn skip(self, n: usize) -> Skip<Self>
where Self: Sized,

Creates a new stream which skips n items of the underlying stream. Read more
source§

fn fuse(self) -> Fuse<Self>
where Self: Sized,

Fuse a stream such that poll_next will never again be called once it has finished. This method can be used to turn any Stream into a FusedStream. Read more
source§

fn by_ref(&mut self) -> &mut Self

Borrows a stream, rather than consuming it. Read more
source§

fn catch_unwind(self) -> CatchUnwind<Self>
where Self: Sized + UnwindSafe,

Catches unwinding panics while polling the stream. Read more
source§

fn boxed<'a>(self) -> BoxStream<'a, Self::Item>
where Self: Sized + Send + 'a,

Wrap the stream in a Box, pinning it. Read more
source§

fn boxed_local<'a>(self) -> LocalBoxStream<'a, Self::Item>
where Self: Sized + 'a,

Wrap the stream in a Box, pinning it. Read more
source§

fn buffered(self, n: usize) -> Buffered<Self>
where Self::Item: Future, Self: Sized,

An adaptor for creating a buffered list of pending futures. Read more
source§

fn buffer_unordered(self, n: usize) -> BufferUnordered<Self>
where Self::Item: Future, Self: Sized,

An adaptor for creating a buffered list of pending futures (unordered). Read more
source§

fn zip<St>(self, other: St) -> Zip<Self, St>
where St: Stream, Self: Sized,

An adapter for zipping two streams together. Read more
source§

fn chain<St>(self, other: St) -> Chain<Self, St>
where St: Stream<Item = Self::Item>, Self: Sized,

Adapter for chaining two streams. Read more
source§

fn peekable(self) -> Peekable<Self>
where Self: Sized,

Creates a new stream which exposes a peek method. Read more
source§

fn chunks(self, capacity: usize) -> Chunks<Self>
where Self: Sized,

An adaptor for chunking up items of the stream inside a vector. Read more
source§

fn ready_chunks(self, capacity: usize) -> ReadyChunks<Self>
where Self: Sized,

An adaptor for chunking up ready items of the stream inside a vector. Read more
source§

fn forward<S>(self, sink: S) -> Forward<Self, S> ⓘ
where S: Sink<Self::Ok, Error = Self::Error>, Self: TryStream + Sized,

A future that completes after the given stream has been fully processed into the sink and the sink has been flushed and closed. Read more
source§

fn split<Item>(self) -> (SplitSink<Self, Item>, SplitStream<Self>)
where Self: Sink<Item> + Sized,

Splits this Stream + Sink object into separate Sink and Stream objects. Read more
source§

fn inspect<F>(self, f: F) -> Inspect<Self, F>
where F: FnMut(&Self::Item), Self: Sized,

Do something with each item of this stream, afterwards passing it on. Read more
source§

fn left_stream<B>(self) -> Either<Self, B> ⓘ
where B: Stream<Item = Self::Item>, Self: Sized,

Wrap this stream in an Either stream, making it the left-hand variant of that Either. Read more
source§

fn right_stream<B>(self) -> Either<B, Self> ⓘ
where B: Stream<Item = Self::Item>, Self: Sized,

Wrap this stream in an Either stream, making it the right-hand variant of that Either. Read more
source§

fn poll_next_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>
where Self: Unpin,

A convenience method for calling Stream::poll_next on Unpin stream types.
source§

fn select_next_some(&mut self) -> SelectNextSome<'_, Self> ⓘ
where Self: Unpin + FusedStream,

Returns a Future that resolves when the next item in this stream is ready. Read more
source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
source§

impl<S, T, E> TryStream for S
where S: Stream<Item = Result<T, E>> + ?Sized,

§

type Ok = T

The type of successful values yielded by this future
§

type Error = E

The type of failures yielded by this future
source§

fn try_poll_next( self: Pin<&mut S>, cx: &mut Context<'_>, ) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>

Poll this TryStream as if it were a Stream. Read more
source§

impl<S> TryStreamExt for S
where S: TryStream + ?Sized,

source§

fn err_into<E>(self) -> ErrInto<Self, E>
where Self: Sized, Self::Error: Into<E>,

Wraps the current stream in a new stream which converts the error type into the one provided. Read more
source§

fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>
where Self: Sized, F: FnMut(Self::Ok) -> T,

Wraps the current stream in a new stream which maps the success value using the provided closure. Read more
source§

fn map_err<E, F>(self, f: F) -> MapErr<Self, F>
where Self: Sized, F: FnMut(Self::Error) -> E,

Wraps the current stream in a new stream which maps the error value using the provided closure. Read more
source§

fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>
where F: FnMut(Self::Ok) -> Fut, Fut: TryFuture<Error = Self::Error>, Self: Sized,

Chain on a computation for when a value is ready, passing the successful results to the provided closure f. Read more
source§

fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>
where F: FnMut(Self::Error) -> Fut, Fut: TryFuture<Ok = Self::Ok>, Self: Sized,

Chain on a computation for when an error happens, passing the erroneous result to the provided closure f. Read more
source§

fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>
where F: FnMut(&Self::Ok), Self: Sized,

Do something with the success value of this stream, afterwards passing it on. Read more
source§

fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>
where F: FnMut(&Self::Error), Self: Sized,

Do something with the error value of this stream, afterwards passing it on. Read more
source§

fn into_stream(self) -> IntoStream<Self>
where Self: Sized,

Wraps a TryStream into a type that implements Stream Read more
source§

fn try_next(&mut self) -> TryNext<'_, Self> ⓘ
where Self: Unpin,

Creates a future that attempts to resolve the next item in the stream. If an error is encountered before the next item, the error is returned instead. Read more
source§

fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F> ⓘ
where F: FnMut(Self::Ok) -> Fut, Fut: TryFuture<Ok = (), Error = Self::Error>, Self: Sized,

Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream. Read more
source§

fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F>
where F: FnMut(&Self::Ok) -> Fut, Fut: TryFuture<Ok = bool, Error = Self::Error>, Self: Sized,

Skip elements on this stream while the provided asynchronous predicate resolves to true. Read more
source§

fn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F>
where F: FnMut(&Self::Ok) -> Fut, Fut: TryFuture<Ok = bool, Error = Self::Error>, Self: Sized,

Take elements on this stream while the provided asynchronous predicate resolves to true. Read more
source§

fn try_for_each_concurrent<Fut, F>( self, limit: impl Into<Option<usize>>, f: F, ) -> TryForEachConcurrent<Self, Fut, F> ⓘ
where F: FnMut(Self::Ok) -> Fut, Fut: Future<Output = Result<(), Self::Error>>, Self: Sized,

Attempts to run this stream to completion, executing the provided asynchronous closure for each element on the stream concurrently as elements become available, exiting as soon as an error occurs. Read more
source§

fn try_collect<C: Default + Extend<Self::Ok>>(self) -> TryCollect<Self, C> ⓘ
where Self: Sized,

Attempt to transform a stream into a collection, returning a future representing the result of that computation. Read more
source§

fn try_chunks(self, capacity: usize) -> TryChunks<Self>
where Self: Sized,

An adaptor for chunking up successful items of the stream inside a vector. Read more
source§

fn try_ready_chunks(self, capacity: usize) -> TryReadyChunks<Self>
where Self: Sized,

An adaptor for chunking up successful, ready items of the stream inside a vector. Read more
source§

fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F>
where Fut: Future<Output = bool>, F: FnMut(&Self::Ok) -> Fut, Self: Sized,

Attempt to filter the values produced by this stream according to the provided asynchronous closure. Read more
source§

fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F>
where Fut: TryFuture<Ok = Option<T>, Error = Self::Error>, F: FnMut(Self::Ok) -> Fut, Self: Sized,

Attempt to filter the values produced by this stream while simultaneously mapping them to a different type according to the provided asynchronous closure. Read more
source§

fn try_flatten_unordered( self, limit: impl Into<Option<usize>>, ) -> TryFlattenUnordered<Self>
where Self::Ok: TryStream + Unpin, <Self::Ok as TryStream>::Error: From<Self::Error>, Self: Sized,

Flattens a stream of streams into just one continuous stream. Produced streams will be polled concurrently and any errors will be passed through without looking at them. If the underlying base stream returns an error, it will be immediately propagated. Read more
source§

fn try_flatten(self) -> TryFlatten<Self>
where Self::Ok: TryStream, <Self::Ok as TryStream>::Error: From<Self::Error>, Self: Sized,

Flattens a stream of streams into just one continuous stream. Read more
source§

fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F> ⓘ
where F: FnMut(T, Self::Ok) -> Fut, Fut: TryFuture<Ok = T, Error = Self::Error>, Self: Sized,

Attempt to execute an accumulating asynchronous computation over a stream, collecting all the values into one final result. Read more
source§

fn try_concat(self) -> TryConcat<Self> ⓘ
where Self: Sized, Self::Ok: Extend<<<Self as TryStream>::Ok as IntoIterator>::Item> + IntoIterator + Default,

Attempt to concatenate all items of a stream into a single extendable destination, returning a future representing the end result. Read more
source§

fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self>
where Self::Ok: TryFuture<Error = Self::Error>, Self: Sized,

Attempt to execute several futures from a stream concurrently (unordered). Read more
source§

fn try_buffered(self, n: usize) -> TryBuffered<Self>
where Self::Ok: TryFuture<Error = Self::Error>, Self: Sized,

Attempt to execute several futures from a stream concurrently. Read more
source§

fn try_poll_next_unpin( &mut self, cx: &mut Context<'_>, ) -> Poll<Option<Result<Self::Ok, Self::Error>>>
where Self: Unpin,

A convenience method for calling TryStream::try_poll_next on Unpin stream types.
source§

fn into_async_read(self) -> IntoAsyncRead<Self>
where Self: Sized + TryStreamExt<Error = Error>, Self::Ok: AsRef<[u8]>,

Adapter that converts this stream into an AsyncBufRead. Read more
source§

fn try_all<Fut, F>(self, f: F) -> TryAll<Self, Fut, F> ⓘ
where Self: Sized, F: FnMut(Self::Ok) -> Fut, Fut: Future<Output = bool>,

Attempt to execute a predicate over an asynchronous stream and evaluate if all items satisfy the predicate. Exits early if an Err is encountered or if an Ok item is found that does not satisfy the predicate. Read more
source§

fn try_any<Fut, F>(self, f: F) -> TryAny<Self, Fut, F> ⓘ
where Self: Sized, F: FnMut(Self::Ok) -> Fut, Fut: Future<Output = bool>,

Attempt to execute a predicate over an asynchronous stream and evaluate if any items satisfy the predicate. Exits early if an Err is encountered or if an Ok item is found that satisfies the predicate. Read more