dyn Trait for Dynamic Dispatch in Rust

pub trait Trait {}

impl Trait for i32 {}
impl Trait for String {}

fn main() {
    let int: &dyn Trait = &42i32;
    let string: &dyn Trait = &("Hello dyn!".to_owned());
}

  • Dynamic Dispatch is a tool in Object Oriented Programming that is often used in places where one needs to care more about the behavior of a type than what the type is.

    In OOP languages, dynamic dispatch is often an implicit process and not something you can opt out of.

    In rust, we use dyn Trait: an opt-in form of dynamic dispatch.

  • For any trait that is dyn compatible we can coerce a reference to a value of that trait into a dyn Trait value.

  • We call these trait objects. Their type is not known at compile time, but their behavior is: what is implemented by the trait itself.

  • When you need OOP-style heterogeneous data structures, you can reach for Box<dyn Trait>, but try to keep it homogeneous and generic-based first!