Code shared from the Rust Playground

playground.rs

use std::collections::HashMap;
use std::fmt::Debug;

pub trait StaticBuilder {
    fn build(&self) -> Box<HasName>;
}

struct UserBuilder;

impl StaticBuilder for UserBuilder {
    fn build(&self) -> Box<HasName> {
        Box::new(User::new())
    }
}

pub fn type_registry() -> HashMap<u16, Box<StaticBuilder>> {
   let mut m: HashMap<u16, Box<StaticBuilder>> = HashMap::new();
   m.insert(1 as u16, Box::new(UserBuilder));
//   m.insert(2 as u16, Box::new(ProfileBuilder));
   m
}

fn main() {
    let type_registry = type_registry();

    let builder = type_registry.get(&(1 as u16)).unwrap();
    println!("{:?}", builder.build());
}

pub trait HasName: Debug {
    fn get_name(&self) -> String;
}

#[derive(Debug)]
struct User {
    name: String
}

impl User {
    fn new() -> Self {
        User {
            name: "jonah".to_string(),
        }
    }
}

impl HasName for User {
    fn get_name(&self) -> String {
        self.name.clone()
    }
}