Rust: What is the difference between trait objects and generics?

Trait objects (dyn) — dynamic dispatch. Generics — static dispatch.

Trait objects:

• Runtime dispatch.
• Fat pointer.
• Flexible.

Generics:

• Compile-time dispatch.
• Monomorphization.
• Faster.

1// Trait object
2fn draw(shape: &dyn Shape) {
3    shape.draw();
4}
5
6// Generics
7fn draw<T: Shape>(shape: &T) {
8    shape.draw();
9}

When to use:

• Trait objects: heterogeneous collections.
• Generics: performance-critical code.

Key: dyn for flexibility, generics for performance.