[−][src]Trait geng_core::prelude::futures::future::TryFutureExt
Adapters specific to Result-returning futures
Provided methods
fn flatten_sink<Item>(self) -> FlattenSink<Self, Self::Ok> where
Self::Ok: Sink<Item>,
<Self::Ok as Sink<Item>>::Error == Self::Error,
Self::Ok: Sink<Item>,
<Self::Ok as Sink<Item>>::Error == Self::Error,
Flattens the execution of this future when the successful result of this
future is a Sink.
This can be useful when sink initialization is deferred, and it is convenient to work with that sink as if the sink was available at the call site.
Note that this function consumes this future and returns a wrapped version of it.
Examples
use futures::future::{Future, TryFutureExt}; use futures::sink::Sink; fn make_sink_async() -> impl Future<Output = Result< impl Sink<T, Error = E>, E, >> { // ... } fn take_sink(sink: impl Sink<T, Error = E>) { /* ... */ } let fut = make_sink_async(); take_sink(fut.flatten_sink())
fn map_ok<T, F>(self, f: F) -> MapOk<Self, F>ⓘ where
F: FnOnce(Self::Ok) -> T,
F: FnOnce(Self::Ok) -> T,
Maps this future's success value to a different value.
This method can be used to change the Ok type of the
future into a different type. It is similar to the Result::map
method. You can use this method to chain along a computation once the
future has been resolved.
The provided closure f will only be called if this future is resolved
to an Ok. If it resolves to an Err, panics, or is dropped, then
the provided closure will never be invoked.
Note that this method consumes the future it is called on and returns a wrapped version of it.
Examples
use futures::future::TryFutureExt; let future = async { Ok::<i32, i32>(1) }; let future = future.map_ok(|x| x + 3); assert_eq!(future.await, Ok(4));
Calling map_ok on an errored future has no
effect:
use futures::future::TryFutureExt; let future = async { Err::<i32, i32>(1) }; let future = future.map_ok(|x| x + 3); assert_eq!(future.await, Err(1));
fn map_err<E, F>(self, f: F) -> MapErr<Self, F>ⓘ where
F: FnOnce(Self::Error) -> E,
F: FnOnce(Self::Error) -> E,
Maps this future's error value to a different value.
This method can be used to change the Error type
of the future into a different type. It is similar to the
Result::map_err method. You can use this method for example to
ensure that futures have the same Error type when
using [select!] or [join!].
The provided closure f will only be called if this future is resolved
to an Err. If it resolves to an Ok, panics, or is dropped, then
the provided closure will never be invoked.
Note that this method consumes the future it is called on and returns a wrapped version of it.
Examples
use futures::future::TryFutureExt; let future = async { Err::<i32, i32>(1) }; let future = future.map_err(|x| x + 3); assert_eq!(future.await, Err(4));
Calling map_err on a successful future has
no effect:
use futures::future::TryFutureExt; let future = async { Ok::<i32, i32>(1) }; let future = future.map_err(|x| x + 3); assert_eq!(future.await, Ok(1));
fn err_into<E>(self) -> ErrInto<Self, E>ⓘ where
Self::Error: Into<E>,
Self::Error: Into<E>,
Maps this future's Error to a new error type
using the Into trait.
This method does for futures what the ?-operator does for
Result: It lets the compiler infer the type of the resulting
error. Just as map_err, this is useful for
example to ensure that futures have the same Error
type when using [select!] or [join!].
Note that this method consumes the future it is called on and returns a wrapped version of it.
Examples
use futures::future::TryFutureExt; let future_err_u8 = async { Err::<(), u8>(1) }; let future_err_i32 = future_err_u8.err_into::<i32>();
fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>ⓘ where
F: FnOnce(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
F: FnOnce(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
Executes another future after this one resolves successfully. The success value is passed to a closure to create this subsequent future.
The provided closure f will only be called if this future is resolved
to an Ok. If this future resolves to an Err, panics, or is
dropped, then the provided closure will never be invoked. The
Error type of this future and the future
returned by f have to match.
Note that this method consumes the future it is called on and returns a wrapped version of it.
Examples
use futures::future::TryFutureExt; let future = async { Ok::<i32, i32>(1) }; let future = future.and_then(|x| async move { Ok::<i32, i32>(x + 3) }); assert_eq!(future.await, Ok(4));
Calling and_then on an errored future has no
effect:
use futures::future::TryFutureExt; let future = async { Err::<i32, i32>(1) }; let future = future.and_then(|x| async move { Err::<i32, i32>(x + 3) }); assert_eq!(future.await, Err(1));
fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>ⓘ where
F: FnOnce(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
F: FnOnce(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
Executes another future if this one resolves to an error. The error value is passed to a closure to create this subsequent future.
The provided closure f will only be called if this future is resolved
to an Err. If this future resolves to an Ok, panics, or is
dropped, then the provided closure will never be invoked. The
Ok type of this future and the future returned by f
have to match.
Note that this method consumes the future it is called on and returns a wrapped version of it.
Examples
use futures::future::TryFutureExt; let future = async { Err::<i32, i32>(1) }; let future = future.or_else(|x| async move { Err::<i32, i32>(x + 3) }); assert_eq!(future.await, Err(4));
Calling or_else on a successful future has
no effect:
use futures::future::TryFutureExt; let future = async { Ok::<i32, i32>(1) }; let future = future.or_else(|x| async move { Ok::<i32, i32>(x + 3) }); assert_eq!(future.await, Ok(1));
fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>ⓘ where
F: FnOnce(&Self::Ok),
F: FnOnce(&Self::Ok),
Do something with the success value of a future before passing it on.
When using futures, you'll often chain several of them together. While
working on such code, you might want to check out what's happening at
various parts in the pipeline, without consuming the intermediate
value. To do that, insert a call to inspect_ok.
Examples
use futures::future::TryFutureExt; let future = async { Ok::<_, ()>(1) }; let new_future = future.inspect_ok(|&x| println!("about to resolve: {}", x)); assert_eq!(new_future.await, Ok(1));
fn inspect_err<F>(self, f: F) -> InspectErr<Self, F>ⓘ where
F: FnOnce(&Self::Error),
F: FnOnce(&Self::Error),
Do something with the error value of a future before passing it on.
When using futures, you'll often chain several of them together. While
working on such code, you might want to check out what's happening at
various parts in the pipeline, without consuming the intermediate
value. To do that, insert a call to inspect_err.
Examples
use futures::future::TryFutureExt; let future = async { Err::<(), _>(1) }; let new_future = future.inspect_err(|&x| println!("about to error: {}", x)); assert_eq!(new_future.await, Err(1));
fn try_flatten_stream(self) -> TryFlattenStream<Self> where
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error == Self::Error,
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error == Self::Error,
Flatten the execution of this future when the successful result of this future is a stream.
This can be useful when stream initialization is deferred, and it is convenient to work with that stream as if stream was available at the call site.
Note that this function consumes this future and returns a wrapped version of it.
Examples
use futures::future::TryFutureExt; use futures::stream::{self, TryStreamExt}; let stream_items = vec![17, 18, 19].into_iter().map(Ok); let future_of_a_stream = async { Ok::<_, ()>(stream::iter(stream_items)) }; let stream = future_of_a_stream.try_flatten_stream(); let list = stream.try_collect::<Vec<_>>().await; assert_eq!(list, Ok(vec![17, 18, 19]));
fn unwrap_or_else<F>(self, f: F) -> UnwrapOrElse<Self, F>ⓘ where
F: FnOnce(Self::Error) -> Self::Ok,
F: FnOnce(Self::Error) -> Self::Ok,
Unwraps this future's ouput, producing a future with this future's
Ok type as its
Output type.
If this future is resolved successfully, the returned future will
contain the original future's success value as output. Otherwise, the
closure f is called with the error value to produce an alternate
success value.
This method is similar to the Result::unwrap_or_else method.
Examples
use futures::future::TryFutureExt; let future = async { Err::<(), &str>("Boom!") }; let future = future.unwrap_or_else(|_| ()); assert_eq!(future.await, ());
fn into_future(self) -> IntoFuture<Self>ⓘImportant traits for IntoFuture<Fut>
impl<Fut> Future for IntoFuture<Fut> where
Fut: TryFuture, type Output = Result<<Fut as TryFuture>::Ok, <Fut as TryFuture>::Error>;
Important traits for IntoFuture<Fut>
impl<Fut> Future for IntoFuture<Fut> where
Fut: TryFuture, type Output = Result<<Fut as TryFuture>::Ok, <Fut as TryFuture>::Error>;Wraps a TryFuture into a type that implements
Future.
TryFutures currently do not implement the
Future trait due to limitations of the
compiler.
Examples
use futures::future::{Future, TryFuture, TryFutureExt}; fn make_try_future() -> impl TryFuture<Ok = T, Error = E> { // ... } fn take_future(future: impl Future<Output = Result<T, E>>) { /* ... */ } take_future(make_try_future().into_future());
fn try_poll_unpin(
&mut self,
cx: &mut Context
) -> Poll<Result<Self::Ok, Self::Error>> where
Self: Unpin,
&mut self,
cx: &mut Context
) -> Poll<Result<Self::Ok, Self::Error>> where
Self: Unpin,
A convenience method for calling TryFuture::try_poll on Unpin
future types.