The fact that you ask why it needs to be inlined means you haven't understood how the feature works. If you did, you'd be a fan. It's a general mechansim that fits Zig perfectly, along with inline for and while.

I understood why. I said it is very non-obvious and opaque at first read, so it might trip up a lot of newcomers.

Surely there's better ways to express interfaces than exploiting a brilliant side-effect of compile time inlining.