Function demux_map_lazy 

pub fn demux_map_lazy<Key, Si, Item, Func>(
    func: Func,
) -> LazyDemuxSink<Key, Si, Func>
where
    Key: Eq + Hash + Debug + Unpin,
    Si: Sink<Item> + Unpin,
    Func: FnMut(&Key) -> Si + Unpin,

Available on crate feature std only.

Creates a LazyDemuxSink that lazily creates sinks on first use for each key.

This requires sinks Si to be Unpin. If your sinks are not Unpin, first wrap them in Box::pin to make them Unpin.