Comment by messe

> You just accept passing it around in every function

In every function that needs to allocate yes. Sometimes, it'll be stored in a struct, but that's rare. And not every function needs to allocate.

> and now passing around another param for io as well?

Yes. Not everything needs to do Io.

You should try reading some idiomatic Zig code. Ghostty would be an example (as would much of the Zig standard library).