Static and Dynamic Dispatch at the same time

main.rs

trait Foo {
    fn bar(&self);
}

impl Foo for &dyn Foo {
    fn bar(&self) {
        (*self).bar();
    }
}

struct Bar;

impl Foo for Bar {
    fn bar(&self) {
        println!("Hello");
    }
}

fn foo<T: Foo>(f: &T) {
    f.bar();
}

fn baz(f: &dyn Foo) {
    foo(&f)
}

fn main() {
    let b = Bar;
    
    foo(&b);
    baz(&b);
}

By implementing a Trait for &dyn Trait (or/and &mut dyn Trait, Box<dyn Trait>), you can allow calling statically dispatched code with a trait-object. This allows reusing the statically dispatched implementation with a dynamically dispatched trait-object. Use with care

Actually this is better:

trait Foo {
    fn bar(&self);
}

impl Foo for &dyn Foo {
    fn bar(&self) {
        (*self).bar();
    }
}

struct Bar;

impl Foo for Bar {
    fn bar(&self) {
        println!("Hello");
    }
}

fn foo<T: Foo>(f: &T) {
    f.bar();
}

fn baz(f: &dyn Foo) {
    foo(&f)
}

fn main() {
    let b = Bar;
    
    foo(&b);
    baz(&b);
}