Classes or structs are inherintly not dynamic size, since the dynamic types are pointers to their heap memory location

[TheLazyCat00]

spec/spec/memory.md

Line 17 in ab9c432

- **`Stack-first placement`.** A class instance lives on the stack unless its size is dynamic or it escapes its creating frame; only dynamically-sized data is forced onto the heap (see §3.5).

[TheLazyCat00]

This applies to all types in zane. Since no type is ever dynamic size, no new types can be either.