How do you structure programs in a language without classes?

Start with C or another procedural language. You can define data with structs and keep the operations on that data as separate functions. For example, instead of calling `node.next()`, you might write `next(node)`. The data and behavior are still organized; they just aren’t bundled into one class.

Polymorphism isn’t required for every design. You can use explicit functions for different types, generic functions, tagged unions, function pointers, interfaces, or compile-time techniques depending on what the language supports. The tradeoff is that behavior may be less implicit than a virtual method call, but the design can also be easier to follow and debug. Also keep in mind that the language and toolchain are still evolving, so learn it as an experiment rather than relying on it immediately for career-critical work.

For a game engine, look into data-oriented design and Entity Component System architecture. Rather than making a deep hierarchy such as `Animal -> Bird`, an entity can hold components like position, movement, or health, while separate systems operate on entities with those components. This favors composition, reuse, and straightforward data access over inheritance.

Try focusing on the operations and data transformations your program needs instead of modeling every concept as a real-world object. Functions can accept structs or references to structs, and the caller only needs to know the relevant types and function signatures. Practicing this in C++ with structs and free functions is a good transition.

Modules and namespaces provide much of the organization that classes are often used for. Put related types and functions into a coherent module, expose a small public interface, and keep implementation details private where the language allows it. You still get encapsulation without requiring a class hierarchy.