fn write_vectored<'a, 'b>(&'a mut self, bufs: &'a [IoSlice<'b>]) -> WriteVectored<'a, 'b, Self>
    where
        Self: Unpin,
    {
        assert_future::<Result<usize>, _>(WriteVectored::new(self, bufs))
    }
Creates a future which will write bytes from `bufs` into the object using vectored
IO operations.

The returned future will resolve to the number of bytes written once the write
operation is completed.
futures-util/src/io/mod.rs