https://ziglang.org/devlog/2024/#2024-11-04
It seems like an interesting idea, but I wish Andrew spent more time fleshing it out with complete examples. I can't tell if the _ characters are eliding values or if that's literally what's in his code.
The underscores mean that it's a non-exhaustive enum. An exhaustive enum is where you list all the names of the possible enum values, and other values are illegal. A non-exhaustive enum means any value in the underlying storage is allowed. So at root this code is creating a bunch of new integer types which are all backed by u32 but which can't be directly assigned or compared to each other. That means you can't accidentally pass a SectionIndex into a function expecting an ObjectFunctionImportIndex, which would be impossible to do if those functions just took raw u32's.
Is that the idea?
You can do the same thing wrapping integers with structs, but enum makes it slightly more concise?
I think in Zig for new types you'd use enums for ints and packed structs for more complex types.