Struct StackFuture

Source
#[repr(C, align(8))]
pub struct StackFuture<'a, T, const STACK_SIZE: usize> { /* private fields */ }
Expand description

A wrapper that stores a future in space allocated by the container

Often this space comes from the calling function’s stack, but it could just as well come from some other allocation.

A StackFuture can be used to emulate async functions in dyn Trait objects. For example:

use embedded_jsonrpc::stackfuture::StackFuture;

trait PseudoAsyncTrait {
    fn do_something(&self) -> StackFuture<'_, (), { 512 }>;
}

impl PseudoAsyncTrait for i32 {
    fn do_something(&self) -> StackFuture<'_, (), { 512 }> {
        StackFuture::from(async {
            // function body goes here
        })
    }
}

async fn use_dyn_async_trait(x: &dyn PseudoAsyncTrait) {
    x.do_something().await;
}

async fn call_with_dyn_async_trait() {
    use_dyn_async_trait(&42).await;
}

This example defines PseudoAsyncTrait with a single method do_something. The do_something method can be called as if it were declared as async fn do_something(&self). To implement do_something, the easiest thing to do is to wrap the body of the function in StackFuture::from(async { ... }), which creates an anonymous future for the body and stores it in a StackFuture.

Because StackFuture does not know the size of the future it wraps, the maximum size of the future must be specified in the STACK_SIZE parameter. In the example here, we’ve used a stack size of 512, which is probably much larger than necessary but would accommodate many futures besides the simple one we’ve shown here.

StackFuture ensures when wrapping a future that enough space is available, and it also respects any alignment requirements for the wrapped future. Note that the wrapped future’s alignment must be less than or equal to that of the overall StackFuture struct.

Implementations§

Source§

impl<'a, T, const STACK_SIZE: usize> StackFuture<'a, T, STACK_SIZE>

Source

pub fn from<F>(future: F) -> Self
where F: Future<Output = T> + Send + 'a,

Creates a StackFuture from an existing future

See the documentation on StackFuture for examples of how to use this.

The size and alignment requirements are statically checked, so it is a compiler error to use this with a future that does not fit within the StackFuture’s size and alignment requirements.

The following example illustrates a compile error for a future that is too large.

// Fails because the future contains a large array and is therefore too big to fit in
// a 16-byte `StackFuture`.
let f = StackFuture::<_, { 16 }>::from(async {
    let x = [0u8; 4096];
    async {}.await;
    println!("{}", x.len());
});

The example below illustrates a compiler error for a future whose alignment is too large.


#[derive(Debug)]
#[repr(align(256))]
struct BigAlignment(usize);

// Fails because the future contains a large array and is therefore too big to fit in
// a 16-byte `StackFuture`.
let f = StackFuture::<_, { 16 }>::from(async {
    let x = BigAlignment(42);
    async {}.await;
    println!("{x:?}");
});
Source

pub fn try_from<F>(future: F) -> Result<Self, IntoStackFutureError<F>>
where F: Future<Output = T> + Send + 'a,

Attempts to create a StackFuture from an existing future

If the StackFuture is not large enough to hold future, this function returns an Err with the argument future returned to you.

Panics

If we cannot satisfy the alignment requirements for F, this function will panic.

Source

pub const fn has_space_for<F>() -> bool

Determines whether this StackFuture can hold a value of type F

Source

pub const fn has_space_for_val<F>(_: &F) -> bool

Determines whether this StackFuture can hold the referenced value

Source

pub const fn has_alignment_for<F>() -> bool

Determines whether this StackFuture’s alignment is compatible with the type F.

Source

pub const fn has_alignment_for_val<F>(_: &F) -> bool

Determines whether this StackFuture’s alignment is compatible with the referenced value.

Trait Implementations§

Source§

impl<T, const STACK_SIZE: usize> Drop for StackFuture<'_, T, STACK_SIZE>

Source§

fn drop(&mut self)

Executes the destructor for this type. Read more
Source§

impl<T, const STACK_SIZE: usize> Future for StackFuture<'_, T, STACK_SIZE>

Source§

type Output = T

The type of value produced on completion.
Source§

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>

Attempts to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more

Auto Trait Implementations§

§

impl<'a, T, const STACK_SIZE: usize> Freeze for StackFuture<'a, T, STACK_SIZE>

§

impl<'a, T, const STACK_SIZE: usize> !RefUnwindSafe for StackFuture<'a, T, STACK_SIZE>

§

impl<'a, T, const STACK_SIZE: usize> Send for StackFuture<'a, T, STACK_SIZE>

§

impl<'a, T, const STACK_SIZE: usize> !Sync for StackFuture<'a, T, STACK_SIZE>

§

impl<'a, T, const STACK_SIZE: usize> !Unpin for StackFuture<'a, T, STACK_SIZE>

§

impl<'a, T, const STACK_SIZE: usize> !UnwindSafe for StackFuture<'a, T, STACK_SIZE>

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> FutureExt for T
where T: Future + ?Sized,

Source§

fn map<U, F>(self, f: F) -> Map<Self, F>
where F: FnOnce(Self::Output) -> U, Self: Sized,

Map this future’s output to a different type, returning a new future of the resulting type. Read more
Source§

fn map_into<U>(self) -> MapInto<Self, U>
where Self::Output: Into<U>, Self: Sized,

Map this future’s output to a different type, returning a new future of the resulting type. Read more
Source§

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

Chain on a computation for when a future finished, passing the result of the future to the provided closure f. Read more
Source§

fn left_future<B>(self) -> Either<Self, B>
where B: Future<Output = Self::Output>, Self: Sized,

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

fn right_future<A>(self) -> Either<A, Self>
where A: Future<Output = Self::Output>, Self: Sized,

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

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

Convert this future into a single element stream. Read more
Source§

fn flatten(self) -> Flatten<Self>
where Self::Output: Future, Self: Sized,

Flatten the execution of this future when the output of this future is itself another future. Read more
Source§

fn flatten_stream(self) -> FlattenStream<Self>
where Self::Output: Stream, Self: Sized,

Flatten the execution of this future when the successful result of this future is a stream. Read more
Source§

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

Fuse a future such that poll will never again be called once it has completed. This method can be used to turn any Future into a FusedFuture. Read more
Source§

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

Do something with the output of a future before passing it on. Read more
Source§

fn unit_error(self) -> UnitError<Self>
where Self: Sized,

Source§

fn never_error(self) -> NeverError<Self>
where Self: Sized,

Source§

fn poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Self::Output>
where Self: Unpin,

A convenience for calling Future::poll on Unpin future types.
Source§

fn now_or_never(self) -> Option<Self::Output>
where Self: Sized,

Evaluates and consumes the future, returning the resulting output if the future is ready after the first call to Future::poll. Read more
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<F> IntoFuture for F
where F: Future,

Source§

type Output = <F as Future>::Output

The output that the future will produce on completion.
Source§

type IntoFuture = F

Which kind of future are we turning this into?
Source§

fn into_future(self) -> <F as IntoFuture>::IntoFuture

Creates a future from a value. Read more
Source§

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

Source§

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<F, T, E> TryFuture for F
where F: Future<Output = Result<T, E>> + ?Sized,

Source§

type Ok = T

The type of successful values yielded by this future
Source§

type Error = E

The type of failures yielded by this future
Source§

fn try_poll( self: Pin<&mut F>, cx: &mut Context<'_>, ) -> Poll<<F as Future>::Output>

Poll this TryFuture as if it were a Future. Read more
Source§

impl<Fut> TryFutureExt for Fut
where Fut: TryFuture + ?Sized,

Source§

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

Maps this future’s success value to a different value. Read more
Source§

fn map_ok_or_else<T, E, F>(self, e: E, f: F) -> MapOkOrElse<Self, F, E>
where F: FnOnce(Self::Ok) -> T, E: FnOnce(Self::Error) -> T, Self: Sized,

Maps this future’s success value to a different value, and permits for error handling resulting in the same type. Read more
Source§

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

Maps this future’s error value to a different value. Read more
Source§

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

Maps this future’s Error to a new error type using the Into trait. Read more
Source§

fn ok_into<U>(self) -> OkInto<Self, U>
where Self: Sized, Self::Ok: Into<U>,

Maps this future’s Ok to a new type using the Into trait.
Source§

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

Executes another future after this one resolves successfully. The success value is passed to a closure to create this subsequent future. Read more
Source§

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

Executes another future if this one resolves to an error. The error value is passed to a closure to create this subsequent future. Read more
Source§

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

Do something with the success value of a future before passing it on. Read more
Source§

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

Do something with the error value of a future before passing it on. Read more
Source§

fn try_flatten(self) -> TryFlatten<Self, Self::Ok>
where Self::Ok: TryFuture<Error = Self::Error>, Self: Sized,

Flatten the execution of this future when the successful result of this future is another future. Read more
Source§

fn try_flatten_stream(self) -> TryFlattenStream<Self>
where Self::Ok: TryStream<Error = Self::Error>, Self: Sized,

Flatten the execution of this future when the successful result of this future is a stream. Read more
Source§

fn unwrap_or_else<F>(self, f: F) -> UnwrapOrElse<Self, F>
where Self: Sized, F: FnOnce(Self::Error) -> Self::Ok,

Unwraps this future’s output, producing a future with this future’s Ok type as its Output type. Read more
Source§

fn into_future(self) -> IntoFuture<Self>
where Self: Sized,

Wraps a TryFuture into a type that implements Future. Read more
Source§

fn try_poll_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.
Source§

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

Source§

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.