use super::assert_stream;

use core::pin::Pin;

use futures_core::stream::Stream;

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

/// Stream for the [`iter`] function.

#[derive(Debug, Clone)]

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

pub struct Iter<I> {

    iter: I,

}

impl<I> Unpin for Iter<I> {}

/// Converts an `Iterator` into a `Stream` which is always ready

/// to yield the next value.

///

/// Iterators in Rust don't express the ability to block, so this adapter

/// simply always calls `iter.next()` and returns that.

///

/// ```

/// # futures::executor::block_on(async {

/// use futures::stream::{self, StreamExt};

///

/// let stream = stream::iter(vec![17, 19]);

/// assert_eq!(vec![17, 19], stream.collect::<Vec<i32>>().await);

/// # });

/// ```

pub fn iter<I>(i: I) -> Iter<I::IntoIter>

where

    I: IntoIterator,

{

    assert_stream::<I::Item, _>(Iter { iter: i.into_iter() })

}

impl<I> Stream for Iter<I>

where

    I: Iterator,

{

    type Item = I::Item;

    fn poll_next(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Option<I::Item>> {

        Poll::Ready(self.iter.next())

    }

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

        self.iter.size_hint()

    }

}