pub trait AsyncVariableWritable {
// Required method
fn poll_write_single(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
byte: u8
) -> Poll<Result<usize>>;
// Provided method
fn poll_write_more(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut WriteBuf<'_>
) -> Poll<Result<usize>> { ... }
}