[qezz]

What I meant by "you need an allocator" is "you need to explicitly pass the allocator of your choice to the function" [if you want to attach some data to the error]. In rust you can simply return anything as error, not only an enum variant.

[tialaramex]

But that's back to idiom. In this case specifically in Zig a common idiom is to pass an allocator to might-allocate functions such as the growable array push function, while in Rust it would be usual to weld the allocator choice to the type itself with a constructor function e.g. Vec::with_capacity_in.