OOP & Trait Objects

This map covers Rust’s object-oriented features: encapsulation, trait-based polymorphism, dispatch choices, and state-pattern designs without class inheritance.

Concepts

• Object-Oriented Rust — how Rust maps OOP goals onto structs, enums, methods, traits, generics, and trait objects.
• Encapsulation in Rust — using privacy and public APIs to protect invariants and hide representation.
• Trait Objects — using dyn Trait behind pointers for runtime polymorphism and heterogeneous values.
• dyn Compatibility (Object Safety) — the rules a trait must follow to be usable as dyn Trait.
• Static vs Dynamic Dispatch — choosing between monomorphized generic calls and runtime trait-object calls.

Patterns

• Composition over Inheritance — building behavior from fields, traits, and delegation instead of parent classes.
• The State Pattern — representing internal runtime states as private trait objects.
• Type-State State Machines — encoding states as distinct types so invalid transitions fail at compile time.

Antipatterns

• Overusing Trait Objects — erasing concrete types when generics, enums, or concrete types would be clearer.
• Non-dyn-Compatible Traits as Trait Objects — trying to use a trait as dyn Trait when its API cannot support dynamic dispatch.

See also

Traits · Generics · Trait Bounds · Dynamically Sized Types · Box · Enums · Making Invalid States Unrepresentable · Default Implementations

Sources

• The Rust Programming Language, ch. 18 “Object-Oriented Programming Features” — the-book, https://doc.rust-lang.org/book/ch18-00-oop.html
• The Rust Reference, “Dyn compatibility” — the-reference, https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility
• The Rust Reference, “Trait object types” — the-reference, https://doc.rust-lang.org/reference/types/trait-object.html