I looked into this recently, and this is the implementation I ended up choosing:

https://github.com/mapbox/variant

It has a very handy "match" method that addresses the issue raised in this blog post.

They've also compiled many links to other variant implementations, as well as a bibliography on the standardisation efforts:

https://github.com/mapbox/variant/blob/master/doc/other_impl...

https://github.com/mapbox/variant/blob/master/doc/standards_...