You've put the

pub fn implBy(impl_obj: anytype) Logger

Function in a weird place. Normal practice is for the specific implementations to have a getLogger function to create the logger. For example, the allocators in Zig have you instantiate the top level and then call .allocator() on them to get the vtable + pointer to self.

It manages sanity a lot better, and the function implementations in the vtable can be private.

Also can add compilation time as an upside to vtables.

And using vtable in code feels cleaner compared to using generics