How Rust Uses Traits to Achieve Polymorphism With Trait Objects

Rust's trait system enables polymorphism by defining shared behavior that multiple structs must implement, functioning similarly to interfaces in languages like Java. A trait can require implementing structs to also satisfy other trait bounds, such as the Debug trait, though bounds like Default are not permitted directly on trait definitions due to compile-time size constraints. Developers can still implement the Default trait on individual structs and use it directly, but it cannot be called on trait objects. By wrapping structs in a Box<dyn TraitThing> smart pointer, Rust allows code to call trait methods on any conforming struct without knowing the concrete type at compile time. This pattern, demonstrated through two structs and an enum selector, illustrates how Rust achieves runtime polymorphism while maintaining its strict type-safety guarantees.