struct Foo {}

fn frob( _ : &Foo ) {}


trait Trait {}

impl Trait for Foo {}

fn dyn_frob( _ : &dyn Trait ) {}


fn main() {
    let foo = Box::new( Foo {} );
    frob( &foo );  // ok

    let dyn_foo : Box<dyn Trait> = foo;
//  dyn_frob( &dyn_foo );
//            ^^^^^^^^ the trait `Trait` is not implemented for `std::boxed::Box<dyn Trait>`
    dyn_frob( &*dyn_foo );  // ok
}