> Google Highway manage to pull it off but the trade off is a variadics interface that I personally find very difficult.

I'm curious what you mean by 'variadics', and what exactly you find difficult?

People new to Highway are often surprised by the d/tag argument to loads that say whether to load half/full vector, or no more than 4 elements, etc. The key is to understand these are just zero-sized structs used for type information, and are not the actual vector/data. After that, I observe introductory workshop participants are able to get started/productive quickly.