use crate::Stream;

use core::marker::PhantomData;

use core::pin::Pin;

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

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

#[derive(Debug)]

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

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

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

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

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

/// Creates a stream that yields nothing.

///

/// The returned stream is immediately ready and returns `None`. Use

/// [`stream::pending()`](super::pending()) to obtain a stream that is never

/// ready.

///

/// # Examples

///

/// Basic usage:

///

/// ```

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

///

/// #[tokio::main]

/// async fn main() {

///     let mut none = stream::empty::<i32>();

///

///     assert_eq!(None, none.next().await);

/// }

/// ```

pub const fn empty<T>() -> Empty<T> {

    Empty(PhantomData)

}

impl<T> Stream for Empty<T> {

    type Item = T;

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

        Poll::Ready(None)

    }

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

        (0, Some(0))

    }

}