Pattern match on traits in Rust

trait_pattern_match.rs

struct Foo{ value: u32 }
struct Bar{ value: u32 }

trait Base<T> {
    fn accept(&self, v: &dyn Visitor<Result = T>) -> T ;
}
impl <T>Base<T> for Foo {
    fn accept(&self, v: &dyn Visitor<Result = T>) -> T {
        v.visit_foo(&self) 
    }
}
impl <T>Base<T> for Bar {
    fn accept(&self, v: &dyn Visitor<Result = T>) -> T {
        v.visit_bar(&self) 
    }
}

trait Visitor {
    type Result;
    fn visit_foo(&self, foo: &Foo) -> Self::Result;
    fn visit_bar(&self, bar: &Bar) -> Self::Result;
}

struct StringVisitor {}
impl Visitor for StringVisitor {
    type Result = String;
    fn visit_foo(&self, foo: &Foo) -> String {
        format!("it was Foo: {:}!", foo.value)
    }
    fn visit_bar(&self, bar: &Bar) -> String {
        format!("it was Bar: {:}!", bar.value)
    }
}
fn test<T>(v: bool) -> Box<dyn Base<T>> {
    if v {
        Box::new(Foo{value: 5})
    } else {
        Box::new(Bar{value: 10}) 
    }
}
fn main() {
    let f = test(true);
    println!("{:}", f.accept( &StringVisitor{} ));
}

Related to https://stackoverflow.com/a/58346517/3012181