use crate::Stream;

use core::marker::PhantomData;

use core::pin::Pin;

use core::task::{Context, Poll};

/// Stream for the [`pending`](fn@pending) function.

#[derive(Debug)]

#[must_use = "streams do nothing unless polled"]

pub struct Pending<T>(PhantomData<T>);

impl<T> Unpin for Pending<T> {}

unsafe impl<T> Send for Pending<T> {}

unsafe impl<T> Sync for Pending<T> {}

/// Creates a stream that is never ready

///

/// The returned stream is never ready. Attempting to call

/// [`next()`](crate::StreamExt::next) will never complete. Use

/// [`stream::empty()`](super::empty()) to obtain a stream that is is

/// immediately empty but returns no values.

///

/// # Examples

///

/// Basic usage:

///

/// ```no_run

/// use tokio_stream::{self as stream, StreamExt};

///

/// #[tokio::main]

/// async fn main() {

///     let mut never = stream::pending::<i32>();

///

///     // This will never complete

///     never.next().await;

///

///     unreachable!();

/// }

/// ```

pub const fn pending<T>() -> Pending<T> {

    Pending(PhantomData)

}

impl<T> Stream for Pending<T> {

    type Item = T;

    fn poll_next(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<T>> {

        Poll::Pending

    }

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

        (0, None)

    }

}