In every different zig project you have to read the source code to see how their specific ad-hoc interface scheme works. Case in point - this article uses a method `pub fn implBy(impl_obj: anytype)` to connect instances to a vtable. The new zig writer uses a `.interface` data member scheme: https://www.openmymind.net/Zigs-New-Writer/ in addition to understanding when and when not to use it.