If you are used to Java: It's like making a class implementing an additional interface from the outside.

    class MyEntity {
      RenderingCache cache;
    }

    now MyEntity implements Drawable {
      void draw(Canvas canvas) {
        this.cache.draw_cached(canvas ...);
      }
    }

Here is some nuance with Rust's OOP relative to java/go/c++: https://stevedonovan.github.io/rust-gentle-intro/object-orie...

If you know haskell, Rust's traits are very similar to type classes, except it also has c++-like generics (templates) and is primarily expression-based like ocaml.

traits vs haskell type classes:

trait -> class struct -> data instance -> impl