In Rust, a dyn trait is a way to specify a trait object with dynamic dispatch.
A trait object is a pointer to an object that implements a trait, and is used when the concrete type of an object is not known at compile time. In other words, it allows you to write code that can work with different types that implement a particular trait without knowing the exact type at compile time.
When defining a trait object in Rust, you can use the dyn keyword to indicate that the trait object should be dynamically dispatched. This means that the specific implementation of the trait for a given object will be determined at runtime rather than at compile time.
For example, consider the following trait definition:
trait MyTrait {
fn my_method(&self);
}To define a trait object with dynamic dispatch, use the dyn keyword:
fn my_function(obj: &dyn MyTrait) {
obj.my_method();
}In this example, my_function takes a reference to a trait object that implements the MyTrait trait, with dynamic dispatch specified using the dyn keyword. This means that at runtime, the specific implementation of my_method for the given object will be determined dynamically.
Using dyn trait allows Rust to provide runtime polymorphism, which is useful in situations where the concrete type of an object is not known at compile time, but needs to be determined at runtime. However, it can come at a performance cost compared to static dispatch, which is resolved at compile time.