use futures_core::future::Future;

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

use futures_io::AsyncWrite;

use std::io;

use std::pin::Pin;

/// Future for the [`flush`](super::AsyncWriteExt::flush) method.

#[derive(Debug)]

#[must_use = "futures do nothing unless you `.await` or poll them"]

pub struct Flush<'a, W: ?Sized> {

    writer: &'a mut W,

}

impl<W: ?Sized + Unpin> Unpin for Flush<'_, W> {}

impl<'a, W: AsyncWrite + ?Sized + Unpin> Flush<'a, W> {

    pub(super) fn new(writer: &'a mut W) -> Self {

        Self { writer }

    }

}

impl<W> Future for Flush<'_, W>

where

    W: AsyncWrite + ?Sized + Unpin,

{

    type Output = io::Result<()>;

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

        Pin::new(&mut *self.writer).poll_flush(cx)

    }

}