ufotofu 0.12.1

Abstractions for lazily consuming and producing sequences
Documentation 
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use core::convert::Infallible;
use core::fmt::Debug;

use either::Either;

use crate::prelude::*;

/// A (bulk) producer that immediately yields a predetermined final value.
///
/// <br/>Counterpart: the [`consumer::Full`] type.
#[derive(Debug, Clone, Copy)]

pub struct Empty<T>(Option<T>);

/// Creates a producer that returns a final value and nothing else.
///
/// ```
/// # use ufotofu::prelude::*;
/// use producer::empty;
/// # pollster::block_on(async {
///
/// let mut p = empty(17);
/// assert_eq!(p.produce().await?, Right(17));
/// # Result::<(), Infallible>::Ok(())
/// # });
/// ```
///
/// <br/>Counterpart: the [consumer::full] function.
pub fn empty<T>(fin: T) -> Empty<T> {
    Empty(Some(fin))
}

impl<T> Producer for Empty<T> {
    type Item = Infallible;
    type Final = T;
    type Error = Infallible;

    async fn produce(&mut self) -> Result<Either<Self::Item, Self::Final>, Self::Error> {
        Ok(Right(self.0.take().expect(
            "Must not call produce after having yielded the final value",
        )))
    }

    async fn slurp(&mut self) -> Result<(), Self::Error> {
        Ok(())
    }
}

impl<T> BulkProducer for Empty<T> {
    async fn expose_items_gracefully<F, R>(
        &mut self,
        f: F,
    ) -> Result<Either<R, (F, Self::Final)>, (F, Self::Error)>
    where
        F: AsyncFnOnce(&[Self::Item]) -> (usize, R),
    {
        Ok(Right((
            f,
            self.0
                .take()
                .expect("Must not call expose_items after having yielded the final value"),
        )))
    }
}